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THE WAR GASES 



CHEMISTRY AND ANALYSIS 



BY 

DR. MARIO SARTORI 

Chemist of the Italian Chemical 
Warfare Service 



Preface by 
PROFESSOR G. BARGELLINI 

of Rome University 



Translated from the Second Enlarged 
Italian Edition by 

L. W. MARRISON, B.Sc, A.I.C. 



With 20 Figures and 15 Tables 




NEW YORK 

D. VAN NOSTRAND CO., INC. 

250 FOURTH AVENUE 
1939 



PREFACE TO THE FIRST ITALIAN 



EDITION 

The world conflict of 1914-18 opened a new field of study in 
the Chemistry of War : that of the war gases. Thus the Chemistry 
of War, which had for its cradle the chemical laboratory in Turin 
where Ascanio Sobrero discovered nitroglycerine and which for 
60 years was confined to the study of explosives, underwent a 
new development and a new orientation when substances which 
had an offensive action on the human and animal organism were 
first used on the field of battle. Then commenced the study of 
war gases which has become one of the most complex and 
important departments of chemistry. 

Our present knowledge of most of these asphyxiating gases is 
very superficial and even inexact, which is the reason that while 
some merit the importance given to them, others tend to be 
overvalued. Books are therefore necessary to give information 
as to what has been published of the constitution, the methods of 
preparation and the properties of these substances. 

While many German, American and Russian treatises elucidate 
this subject, which is of such great and present interest, in a wide 
and complete manner, few publications exist on the subject in the 
Italian language. Dr. Sartori's book therefore fills a lacuna in 
our scientific bibliography. 

This book by my pupil, which I present to the Italian public, 
is a complete account of the information and facts obtained with 
scrupulous diligence from very various sources, explained with 
clarity and scientific precision, so that it constitutes a trustworthy 
and practical work of reference for chemists and of information 
for students of this subject. 

PROFESSOR GUIDO BARGELLINI. 



V 



INTRODUCTION 



The date of the commencement of scientifically organised 
chemical warfare is universally fixed at April 22nd, 1915, when 
the Germans launched the first cloud of chlorine gas in the region 
of Ypres. 

It may be said that on the same date the study of the war gases 
commenced. In the literature of the pre-war period, occasional 
notes appear concerning the physical, chemical and biological 
properties of most of the substances which were employed in the 
European War as war gases. These notes, however, were not the 
result of systematic researches, at any rate from the biological 
side, but of inquiries into accidents. 

A complete study of only a few substances was in existence, 
but these were more properly poisons, such as the alkaloids and 
the arsenic-containing pharmaceuticals, etc., and cannot be 
included among the war gases. 

The employment of noxious substances as munitions of war 
imposed on chemists of all nations the necessity of co-ordinating 
and adding to the existing data concerning substances which were 
both toxic and also had the necessary physical, chemical and 
technical properties. These researches were concerned both 
with the manufacturing processes best suited to the national 
resources and with the most efficient methods of employing 
substances already known to be toxic. Furthermore, the biological 
properties of known substances were defined so as to correlate 
offensive action with chemical structure, and finally, especially 
at the end of the war and in the post-war period, new war gases 
were synthesised whose employment would surprise the enemy 
and which would also be superior in some respects to those 
already in use. 

In these researches several thousand substances were examined 
during the war, and Edgewood Arsenal, U.S.A., alone examined 
some 4,000. But, of all these, only 54, according to American 
data, were tried in the field, and only 12 were being actually 
used at the end of the war. 

This selection, which was made on the basis of the actual 
conditions in which the substances were employed, shows how 
rigorous are the physical, chemical and technical requirements 

vii 



viii 



INTRODUCTION 



of a substance for it to be utilisable in the field. Substances 
which are satisfactory from the biological point of view must also 

(i) Be capable of being manufactured by practicable and 
economical methods with due regard to national resources. 

And (2) possess physical and chemical properties which render 
them utilisable in the field. 

Studies carried out during and since the war have shown that 

(a) Not all substances harmful to the human organism can be 
used as war gases. 

(b) The most efficient war gases are organic compounds, 
the inorganic compounds which have great toxicity being 
unsuitable for use owing to their physical and chemical properties. 

The war of 1914-18 thus initiated a new branch of chemistry, 
predominantly organic, which only to a limited extent borders on 
toxicological chemistry. 

Work in this new field of study is characterised both by 
experimental difficulty and by the necessity of co-ordinating 
chemical facts with physiopathological data and techno-military 
requirements. 

It is with the confidence of being able to contribute modestly 
to a wider knowledge of the war gases and in the hope of satisfying 
requests for a book which should contain all the purely chemical 
data, at present published in the various manuals of chemical 
warfare in fragmentary or summary form, that I have collected 
in this volume all the best and most recent work published up to 
the present on the chemistry of the war gases. 



CONTENTS 



PAGE 

Preface by Professor G. Bargellini v 

Introduction ........ vii 

PART I 

CHAPTER 

I. The Principal Properties of the War Gases . i 

A. Physiopathological Properties i 

1. The Lower Limit of Irritation ... 2 

2. The Limit of Insupportability ... 2 

3. The Mortality-product (The Lethal Index). 3 

B. Physical Properties ...... 4 

1. Vapour Tension 4 

2. Volatility ....... 6 

3. Boiling Point 8 

4. Melting Point ...... 10 

5. Persistence ....... 10 

C. Chemical Properties ...... 12 

1. Stability to Atmospheric and Chemical 

Agencies ....... 12 

2. Stability on Storage ..... 13 

3. Stability to Explosion ..... 14 

4. Absence of Attack on Metals ... 14 

II. Relation between Chemical Structure and Aggres- 

sive Action ...... 15 

1. Influence of Halogen Atoms ... 15 

2. Influence of the Sulphur Atom ... 17 

3. Influence of the Arsenic Atom ... 18 

4. Influence of the Nitro Group ... 20 

5. Influence of the — CN Group ... 21 

6. Influence of Molecular Structure . . 22 

7. Theories of General Nature ... 23 

Meyer's Theory 23 

Toxophor Auxotox Theory • . . -24 

III. Classification of the War Gases .... 27 

1. Physical Classification ..... 27 

2. Tactical Classification ..... 27 

3. Physiopathological Classification. . . 28 

4. Chemical Classification .... 29 

(a) Jankovsky's Classification ... 29 

(b) Engel's Classification .... 32 



x CONTENTS 

PART II 

CHAPTER PAGE 

IV. The Halogens ....... 33 

1. Chlorine ....... 33 

2. Bromine ........ 37 

Analysis of the Halogens 40 

V. Compounds of Divalent Carbon .... 44 

1. Carbon Monoxide 45 

2. Iron Pentacarbonyl ..... 47 

3. Dibromoacetylene ...... 50 

4. Diiodoacetylene ...... 52 

Analysis of Compounds of Divalent Carbon . 53 

VI. Acyl Halogen Compounds 57 

1. Phosgene, or Carbonyl Chloride ... 59 

2. Carbonyl Bromide ..... 74 

3. Chloroformoxime ...... 76 

4. Dichloroformoxime ..... 77 

5. Oxalyl Chloride ...... 79 

Analysis of the Acyl Halogen Compounds . 81 

VII. Halogenated Ethers 91 

1. Dichloromethyl Ether ..... 92 

2. Dibromomethyl Ether ..... 96 
Analysis of the Halogenated Ethers . . 98 

VIII. Halogenated Esters of Organic Acids ... 99 

A. The Methyl Formate Group .... 99 

1. Methyl Formate ...... 100 

2. Methyl Chloro formate ..... 101 

3. Mono-, Di- and Tri-chloromethyl Chloro- 

formates ....... io4 

4. Hexachloromethyl Carbonate . . . 115 

B. The Ethyl Acetate Group . . . -117 

1. Ethyl Chloroacetate 117 

2. Ethyl Bromoacetate . . . . .119 

3. Ethyl Iodoacetate ..... 121 
Analysis of the Halogenated Esters of Organic 

Acids ........ 123 

IX. Aromatic Esters .127 

1. Benzyl Chloride ...... 129 

2. Benzyl Bromide ...... 132 

3. Benzyl Iodide ...... 134 

4. Ortho-nitrobenzyl Chloride .... 135 

5. Xylyl Bromide ...... 136 

Analysis of the Aromatic Esters . . . 138 



CONTENTS 



XI 



CHAPTFR PAGE 

X. Aldehydes ........ 140 

Acrolein ........ 140 

XI. Halogenated Ketones 146 

A. Aliphatic ........ 146 

1. Chloroacetone ...... 148 

2. Bromoacetone ...... 150 

3. Bromomethyl Ethyl Ketone . . . 153 

B. Aromatic 154 

1. Chloroacetophenone ..... 155 

2. Bromoacetophenone 161 

XII. Halogenated Niiro- Compounds .... 163 

1 Trichloronitrosomethane .... 164 

2. Chloropicrin ....... 165 

3 Tetrachlorodinitroethane .... 173 

4. Bromopicrin 174 

Analysis of the Halogenated Nitro-compounds 176 

XIII. Cyanogen Compounds ...... 181 

1. Hydrocyanic Acid ...... 181 

2. Cyanogen Fluoride ..... 187 

3. Cyanogen Chloride 188 

4. Cyanogen Bromide ..... 191 

5. Cyanogen Iodide ...... 194 

6. Bromobenzyl Cyanide ..... 196 

7. Phenyl Carbylamine Chloride . . . 200 
Analysis of the Cyanogen Compounds . . 204 

XIV. Sulphur Compounds 211 

A. Mercaptans and their Derivatives . . . 211 

1. Perchloromethyl Mercaptan . . . 211 

2. Thiophosgene ...... 213 

B. Sulphides (Thioethers) and thfir Dfrivaiivls . 214 

1. Dichloroethyl Sulphidj- (Mustard Gas) . 217 

2. dlbromoethyl sulphide .... 243 

3. dliodofthyl sulphide 244 

Analysis of the Sulphides (Thioethers) . . 246 

C Chloro Anhydrides and Esters of Sulphuric Acid 253 

1. Chlorosulphonic Acid ..... 255 

2. Sulphuryl Chloride ..... 258 

3. Methyl Sulphuric Acid .... 261 

4. Dimethyl Sulphate ..... 262 

5. Methyl Fluorosulphate .... 266 

6. Mfthyl Chlorosulphate .... 266 

7. Ethyl Chlorosulphate ..... 268 
Analysis of the Sulphuric Acid Derivatives . 269 



xii CONTENTS 

CHAPTER TAC.E 

XV. Arsenic Compounds ...... 271 

A. Aliphatic Arsines ...... 272 

1. Methyl Dichloroarsine .... 273 

2. Ethyl Dichloroarsine ..... 279 

3. Chlorovinyl Arsines (Lewisite) . . . 284 

B. Aromatic Arsines ...... 297 

1. Phenyl Dichloroarsine ..... 298 

2. dlphenyl chloroarsine ..... 302 

3. dlphenyl bromoarsine ..... 314 

4. dlphenyl cyanoarsine ..... 314 

C. Heterocyclic Arsine ...... 318 

1. Phenarsazine Chloride (Adamsite) . . 320 

Tables 336 

Author Index ....... 342 

Subject Index 347 



2 PRINCIPAL PROPERTIES OF THE WAR GASES 



The degree of toxicity is usually expressed by the following 
characteristics : 1 

(1) The lower limit of irritation. 

(2) The limit of insupportability. 

(3) The mortality-product. 

1. The Lower Limit of Irritation 

The lower limit of irritation of a gas, also termed " the threshold 
value of pathological sensitivity," 2 is the minimum concentration 
provoking a painful sensation at those surfaces on which it acts 
in its characteristic manner. The surfaces are the conjunctiva, 
the nasal mucosa and the pharynx, the skin, etc. Experiments 
are made on human subjects and are continued until the appear- 
ance of signs of the specific action of the gas, generally lachryma- 
tion or sneezing, on all or nearly all the persons taking part in the 
experiment. 

The lower limit of irritation is generally expressed in mgm. of 
substance per cubic metre of air. 

In Table I the values of the lower limit of irritation are given 
for several substances. 

Table I. Lower Limits of Irritation 



WAR GAS MGM./CU. M. 

Diphenyl chloroarsine . . . . o-i 

Chloro acetophenone ..... 0-3 

Ethyl dichloroarsine 1 

Chloropicrin ...... 2 

Phosgene 5 

Trichloromethyl chloroformate ... 5 

Dichloromethyl ether . . . 14 



It will be seen from this table that the lower limit of irritation 
of the war gases may vary between fairly wide limits. The 
substance with the greatest irritant power known to the present 
is diphenyl chloroarsine. 

2. The Limit of Insupportability 

The limit of insupportability is the maximum concentration 
which a normal man can support for 1 minute without injury. 
This characteristic can only be determined for those war gases 
which have a predominantly irritant action. In the case of 

1 Detailed accounts of the methods of determining these characteristics are 
given in Lustig, Patologia e clinica delle malattie da gas di guerra, Milan, I937, 
and in Aksenov, Metodika Toksikologii boevikh otravliajuscisch vescestv, Moscow, 
i93i- 

a Ferri and Madesini, Giornale di Medicina Militare, January, 1936, 36. 



PHYSIOPATHOLOGICAL PROPERTIES 



lachrymatories, it is usual after abundant lachrymation to arrive 
at a condition of photophobia, burning of the eyes and inability 
to keep the eyes open, and this stage is considered that of the 
limit of insupportability. In the case of sternutators, in- 
supportability is taken to be the stage when, after the production 
of sneezing, other symptoms such as coughing, retrosternal pain, 
headache, etc., appear and produce the sensation of having 
reached a limit beyond which it would be unwise to proceed. 

In Table II the values of the limits of insupportability are 
given for several substances : 

Table II. Limits of Insupportability 

WAR GAS MGM./CU. M. 

Diphenyl chloroarsine i 

Chloroacetophenone 4-5 

Ethyl dichloroarsine 10 

Dichloromethyl ether . . . .40 
Trichloromethyl chloroformate . . 40 
Chloropicrin 50 

The substance having the lowest limit of insupportability is 
diphenyl chloroarsine, and that having the highest is chloropicrin. 

3. The Mortality-product 

The mortality-product, also termed the Lethal Index, or the 
Haber Product, W, is given by the product of the concentration, C, 
of the substance in air (expressed in mgm. per cu. m.), by the 
duration, t, of its action (expressed in minutes) sufficient to cause 
death. It is normally expressed by the following equation : 

Cxt = W 

The mortality-product gives the toxic power of the asphyxiants 
and of those poisons absorbed through the skin. It cannot be 
experimentally determined on the human subject, and experiments 
are normally made on animals, cats, rabbits, cavies or dogs. 

It is inversely proportional to the toxicity of a substance : 
the lower the value of the index, the greater is the toxic power. 

According to Flury, 1 the formula quoted above gives values 
sufficiently accurate for practical purposes when working with 
concentrations insufficient to cause the death of the animals in a 
few minutes and not so low as to need less than several mgm. of 
the substance. 

American workers have generally determined the mortality- 

1 Flury, Z. ges. expt. Med., 1921, 13, 1, and Gasschutz und Luftschutz, 1932, 
149. 

1—2 



4 PRINCIPAL PROPERTIES OF THE WAR GASES 



product at two different durations : at an exposure time of 
10 minutes (short exposure) and at an exposure time of 30 
minutes (long exposure). 

The values of the mortality-products are referred to the 
species of animal used in the experiments and are valid only 
under the same experimental conditions. They are thus not 
applicable to man. However, they give comparative data of 
great importance for the evaluation of the relative toxic power of 
substances. 

Table III gives values of the mortality-product for several 
substances. 



Table III. Mortality-product 



WAR GAS 


GERMAN DATA 
ON CATS 1 


AMERICAN DATA 
ON DOGS AND 
MICE 2 


Phosgene ..... 


450 


5,000 


Trichloromethyl chloroformate 


500 


5,000 


Dichloromethyl ether 


500 


4,700 


Chloropicrin .... 


2,000 


20,000 


Ethyl dichloroarsine 


3.000 


5,000 


Diphenyl chloroarsine . 


4.000 


I5,0OO 


Chloroacetophenone 


4.000 


8,500 



The difference between the German and the American results 
in Table III is attributable to various causes 3 : the German 
values were obtained with cats, and the American with dogs and 
mice ; cats are more sensitive to some toxic substances and less 
to others ; the German values were obtained during the war, 
when the cats used in the experiments were suffering from 
malnutrition. 

(B) PHYSICAL PROPERTIES 

The principal physical properties to be considered in evaluating 
the practical utility of a substance for use as a war gas are as 
follows : 

1. Vapour Tension 

All liquid and solid substances possess a definite tendency to 
pass into the gaseous condition. Because of this tendency, a 
layer of vapour forms above each substance and exercises a certain 

1 Meyer, Die Grundlagen des Luftschutzes , Leipzig, 1935. 

2 Prentiss, Chemicals in War, New York, 1937. The values quoted refer to 
an exposure period of 10 minutes. 

3 Flury, loc. cit., and Wirth, Gasschutz und Luftschutz, 1936, 250. 



VAPOUR TENSION 



5 



pressure whose magnitude depends on the temperature. This 
pressure, termed the vapour tension or vapour pressure, is 
expressed in mm. of mercury. 

In the case of the war gases, this physical constant has an 
especial interest. In order to be of use in warfare, at least as a 
toxic agent on the respiratory tract, a gas must have a vapour 
pressure high enough at ordinary temperatures to supply enough 
gas to the atmosphere to produce useful physiopathological 
effects. However, this property has only a minor value in the 
case of substances such as diphenyl dichloroarsine, which are 
used in the form of aerosols. 

There are various methods (static, dynamic, etc.) of determining 
the vapour tension of a substance, but it is not proposed to 
describe these here, as they may be found in special treatises. 1 
Moreover, various formulae may be employed to calculate the 
vapour tension of a substance at different temperatures. That 
in most general use is the empirical formula of Regnault 2 : 

log/) = a + b (3< + cy* 

This may also be used in the following shorter form 3 : 

B 

logio^ = A + — 

273 + * 

In this formula A and B are two constants which vary from 
substance to substance and whose values may be calculated from 
the boiling points of the substance, t x and t 2 , at two different 
pressures, p x and p 2 . Two equations are thus obtained with two 
unknowns : 



lo SuPi = A + 



log l0 A = A + 



B 



B 

273 + h 



from which the values of A and B may be obtained. 

Research carried out by various workers has demonstrated 
that this formula gives values sufficiently concordant with those 
obtained experimentally by the dynamic method. In calculating 

1 Ostwald-Luther, Physico-chemischen Messungen, Leipzig, 1925. 

2 Winkelmann, Handbuch der Physik, III, 1906, 950. 

8 Baxter and Bezzenberger, /. Am. Chem. Soc, 1920, 42, 1386 ; Herbst, 
Kolloidchem. Beihefte, 1926, 23, 323 ; Mumford and coll., /. Chem. Soc, 1932, 
589 ; Libermann, Khimija i Tecnologija Otravljajuscikh Vescestv, Moscow, 1931. 



6 PRINCIPAL PROPERTIES OF THE WAR GASES 



the values of the two constants it is necessary, however, to employ 
two boiling points at temperatures at least 70° C. apart. 

Baxter, Mumford and others, 1 applying this formula to the 
determination of the vapour tension of war gases, have determined 
the values of A and B for various substances as follows : 



Table IV. Values of Constants A and B 





A. 


B. 


Phosgene 


7-5595 


— 1,326 


Chloropicrin .... 


8-2424 


— 2,045-I 


Cyanogen bromide 


10-3282 


- 2,457-5 


Dichloromethyl sulphide 


8-3937 


- 2,734-5 


Methyl dichloroarsine . 


8-6944 


— 2,281-7 


Diphenyl chloroarsine . 


7-8930 


- 3,288 



By substituting the values of Table IV in the formula already 
given, the vapour tensions of the various substances may be found 
at different temperatures. 

In Table V the values of the vapour tensions of several 
substances are given in mm. of mercury at 20° C. 



Table V. Vapour Tension at 20° C. 

MM. MERCURY 



Bromobenzyl cyanide .... 0-012 

Dichloroethyl sulphide . . . 0-115 

Chlorovinyl dichloroarsine . . . 0-395 

Trichloromethyl chloroformate . . 10-3 

Chloropicrin ..... 16-9 

Cyanogen chloride .... 1,001-0 

Phosgene i,i73 - 4 



It is seen from this table that the variation in the vapour 
tensions of the war gases is very great. For example, some of these 
substances have a vapour tension greater than one atmosphere 
(phosgene, cyanogen chloride), while others (dichloroethyl 
sulphide, bromobenzyl cyanide) have an extremely low vapour 
tension, and for this reason special methods are necessary in 
order to obtain efficient results in using them in warfare. 

2. Volatflity 

By the term volatility is meant the weight of the substance 
contained in 1 cu. m. of saturated vapour at a certain temperature. 



1 See the preceding note. 



VOLATILITY 



7 



The volatility is usually expressed in mgm. of the substance 
per cu. m. of air, though occasionally also in cu. mm. per cu. m. of 
air. From the latter value the weight per unit volume may be 
calculated from the formula : 

mgm. = cu. mm. x d 

in which d is the density of the substance. 

The volatility is one of the most important factors in the 
selection and evaluation of war gases. 

The volatility V of a substance at a certain temperature t may 
be easily calculated from the following relation : 

M - 273 • p • io 6 

22.4 (273 + t) 7 6 ° 

in which M = molecular weight of the substance, in gm. 

P = vapour tension in mm. of mercury of the substance 
at the temperature t. 

In the following table, values of the volatility are given in 
mgm. of substance per cu. m. of air of some war gases at 20° C. 

Table VI. Volatility at 20° C. 



MGM./CU. M. 

Diphenyl cyanoarsine .... 0-17 
Diphenyl chloroarsine .... o-68 
Dichloroethyl sulphide . . . 625-00 
Benzyl bromide ..... 2,400-00 
Trichloromethyl chloroformate . . 26,000-00 
Methyl dichloroarsine .... 74,400-00 
Chloropicrin ..... 184,000-00 



As is seen from Table VI, the values vary over a wide range ; 
while diphenyl chloroarsine at 20° C. has a volatility of only 
o-68 mgm. per cu. m. of air, at the same temperature the volatility 
of chloropicrin is 184,000 mgm. per cu. m. of air. Because of 
these differences in volatility, the various war gases are used for 
different types of objective and applied by different methods. 

As already noted, the volatility of the war gases varies with 
temperature. Herbst 1 has established the following approximate 
relationship between temperature and volatility : 

Between 10° and 30° C. an increase in temperature of 1° C. causes 
an increase in volatility of about 10%. 

Experimental values of the volatility of dichloroethyl sulphide 

1 Herbst, Kolloidchem. Beihefte, 1926, 23, 340. 



8 PRINCIPAL PROPERTIES OF THE WAR GASES 

between 15 0 and 25° C. are compared in the following table with 
values calculated from Herbst's rule : 



Table VII. Volatility of Dichloroethyl Sulphide 



TiiMFisKAl UKh 


VOLATILITY IN MGM./CU. M. 


°c. 


FOUND 


CALCULATED 


15 


40I 


40I 


16 


439 


441 


x 7 


480 


482 


18 


525 


528 


19 


573 


577 


20 


625 


630 


21 


682 


687 


22 


743 


750 


23 


810 


817 


24 


881 


891 


25 


958 


969 



The increase in volatility caused by increase in temperature 
is very effective in bringing about useful effects from the offensive 
point of view, especially in the case of relatively involatile 
substances. 

3. Boiling Point 

The boiling point of a substance is that temperature at which 
its vapour tension attains the value of the atmospheric pressure. 
The lower the boiling point of a substance, the higher is its 
vapour tension and its volatility. 

Table VIII. Boiling Points of some War Gases at a 
Pressure of 760 mm. of Mercury 



°c. 

Chlorine — 33-5 

Phosgene ...... 8-2 

Hydrocyanic acid ..... 26-5 

Cyanogen bromide . . . . .61 

Monochloromethyl chloroformate . . 107 
Chloropicrin ...... 112 

Dichloroethyl sulphide .... 217 

Chloroacetophenone .... 245 



The war gases have very varied boiling points, as is seen from 
Table VIII. This variation in the boiling points, together with 
the differences in physiopathological action, explains the variation 
between the types of employment which the war gases find in 



BOILING POINT 



9 



warfare. Thus substances with a relatively low boiling point are 
employed in the field when a high gas concentration is required 
for a short time, while those with a rather high boiling point are 
used when a prolonged action is desired. 

According to Herbst, a knowledge of the boiling point of a 
substance enables deductions to be made regarding its volatility. 
In the following table volatilities at 20 0 C. are given corresponding 
with a series of boiling points. 



Table IX. Relation between Boiling Point and Volatility 



B.P. AT 760 MM. 


VOLATILITY AT 20° 


B.P. AT 760 MM. 


VOLATILITY AT 20° 


•c. 


MGM./CU.M. 


°C. 


MGM./CU.M. 


300 


3 


I9O 


2.000 


290 


6 


I8O 


4.500 


280 


12 


I7O 


9,000 


270 


25 


l60 


I4,000 


260 


50 


I50 


21,000 


250 


100 


I4O 


31,000 


24O 


200 


I3O 


46,000 


230 


380 


120 


68,000 


220 


630 


I IO 


100,000 


2IO 


1,000 


IOO 


155,000 


200 


i,550 







From these values, Herbst 1 deduces the following rule concern- 
ing the relation between boiling point and the volatility at 20° C. 

(a) For boiling points between 300° and 230° C, a diminution 
in boiling point of 10° C. corresponds to a doubling of the 
volatility. 

(b) For boiling points below 230 0 C, a diminution in boiling 
point of io° C. corresponds to an increase in volatility of 1-5 to 
i-6 times. 

The boiling point is an important characteristic of a war gas, 
not only because of its connection with vapour tension and there- 
fore with the tactical aims attainable in warfare, but also because 
of its influence on the ease of storage and transport of the 
substance. A war gas whose boiling point is lower than ordinary 
temperatures, as, for example, phosgene, is difficult to pack and 
necessitates the use of refrigerating apparatus during transport 
in order to keep it below its boiling point. 

The preference of the Germans during the war of 1914-18 for 
employing trichloromethyl chloroformate (diphosgene) rather than 

1 Herbst, loc. cit. 



io PRINCIPAL PROPERTIES OF THE WAR GASES 



phosgene was due to the difficulties of manipulating the latter 
gas, owing to its low boiling point. 

4. Melting Point 

The melting point of a substance is the temperature at which 
the solid and the liquid phases of the substance are in equilibrium. 

Table X. Melting Points of some War Gases 

° c. 

Chlorine 102 

Chloropicrin — 69 

Trichloromethyl chloroformate . . — 57 
Hydrocyanic acid . . . . — 15 
Dichloroethyl sulphide . . . + 14-4 
Chloroacetophenone . . . . + 58 

The melting point is an important factor in the use of a gas in 
warfare, for on it depends the practicability of its employment. 
It is easily understood that substances which are quite suitable 
for use with respect to their action in the vapour state cannot be 
efficiently employed in cold regions if they have a high melting 
point, without having recourse to special methods such as 
admixture with other substances so as to reduce the melting 
point. Thus in the case of dichloroethyl sulphide, which in the 
pure state melts at about 14° C, a solution of this substance in 
chlorobenzene was widely used during the war. The melting 
points of mixtures of dichloroethyl sulphide (of 94-95% purity ; 
m.p. 13-4° C.) with chlorobenzene and with carbon tetrachloride 
in various proportions are given in the following table : 



% Solvent 


Chlorobenzene 


Carbon 
tetrachloride 


O 
IO 
20 
30 


m.p. 

13-4° 
8-4° 

6-4° 
-i-o° 


m.p. 

13-4° 
9-8° 
6-6° 
3-i° 



As will be seen, chlorobenzene, which was more commonly 
employed for this purpose, forms mixtures whose melting points 
are lower than the corresponding mixtures containing carbon 
tetrachloride. 

5. Persistence 

The persistence is the time during which a substance can 
continue to exercise its action in an open space. 



PERSISTENCE 



ii 



Among the numerous factors which influence the persistence 
of a gas, the most important are the speed of evaporation of the 
substance, the temperature of the air and the chemical and 
physical nature of the ground. 

Leitner 1 has proposed the following formula for calculating the 
persistence of a war gas : 

\ I M i T 
P V M T x 

S is the persistence of the substance. 

C is the velocity of evaporation of the substance at absolute 

temperature T. 
C x is the velocity of evaporation of water at 15° C. 
p is the vapour tension of the substance at T. 
Pi is the vapour tension of water at 15° C. = 127 mm. 
M is the molecular weight of the substance. 
Mj is the molecular weight of water = 18. 
T is the absolute temperature of the air. 
T i is the absolute temperature corresponding to 15° C. 

This formula gives accurate values for the time which a 
substance takes to evaporate compared with the time taken by 
the same quantity of water at 15° C. in the same conditions. 

In the following table the values of the persistences of several 
war gases are given at various temperatures (persistence of water 
at 15° C. = 1) calculated according to Leitner's formula : 



Table XI. Persistences of some War Gases 









Temperature c 


C. 








— 10 


- 5 


0 


+ 5 


+ 10 


+ 15 


+20 


+ 25 


+3° 


Phosgene 


0'0i4 


0012 


O'OI 


0008 












Chloropicrin . 


i'3° 


098 


0-72 


o-54 


0-4 


o-3 


023 


018 


0-14 


Trichloromethyl 




















chloroformate 


27 


19 


i-4 


I-O 


0-7 


o-5 


04 


03 


0-2 


Lewisite 


96 


63-1 


42- 1 


28-5 


196 


136 


96 


69 


5 


Dichloroethyl 


















sulphide (liquid) . 












103 


67 


44 


29 


Dichloroethyl 




















sulphide (solid) . 


2,400 


1,210 


630 


333 


181 










Bromobenzyl 




















cyanide 


6,93° 


4,1 10 


2,490 


1.530 


960 


610 


395 


260 


173 



1 Leitner, Militarwissensch. u. Techn. Mitteil, 1926, 662. 



c 

in which : 



12 PRINCIPAL PROPERTIES OF THE WAR GASES 



However, Nielson's work 1 shows that these data have only an 
approximate value and indicate merely the order of magnitude 
of the persistence. Nielson observed, inter alia, that in Leitner's 
formula the time of evaporation of a substance is compared with 
that of water into a dry atmosphere, whereas in practice the 
atmosphere always contains a certain amount of water which 
retards the velocity of evaporation. Nevertheless, the data for 
persistence obtained from Leitner's formula, though they have 
only an approximate value, are of interest from the practical point 
of view, for they allow values of the persistences of different gases 
to be compared. For example, from Table XI it is seen that the 
relative persistences of dichloroethyl sulphide and lewisite at 
25° C. are as 44 is to 6-9, and this signifies that at this temperature 
dichloroethyl sulphide is about six times as persistent as 
lewisite. 

These values, it will be understood, indicate only the persistences 
independently of the atmospheric conditions, and of the stability 
of the substances to humidity, and to the physical structure and 
condition of the ground. 

With regard to the last factor, Leitner has specified that the 
values of the persistences given above refer to substances spread 
on " open flat land in dry weather." They may be doubled if 
the substance lies on " broken ground " and tripled if it is in 
" wooded country." 

(C) CHEMICAL PROPERTIES 

The most important chemical properties to be considered in 
evaluating the practical possibilities of a substance for warfare 
are : 

1. Stability to Atmospheric and Chemical Agencies 

From the chemical point of view a war gas must be sufficiently 
resistant to the various agents into which it may come into 
contact in practice. It is especially important that it should be 
indifferent to atmospheric agencies. In the first place, all these 
substances must be indifferent to atmospheric oxygen. However, 
a large number are decomposed more or less rapidly by the action 
of atmospheric humidity, and almost all are decomposed in time 
by rain. 

Rona 2 has made some experiments on the decomposition of 
war gases by water. He has demonstrated experimentally that 
some substances are rapidly decomposed by water (phosgene, 

1 B. Neilsen, Z. ges. Schiess.-Sprengstoffw., 1931, 26, 420. 

2 Rona, Z. ges. expt. Med., 1921, 13, 16. 



CHEMICAL STABILITY 



13 



dichloromethyl ether, etc.), others decompose slowly (dichloroethyl 
sulphide), others only very slowly (benzyl bromide, benzyl iodide, 
xylyl bromide, etc.), while some are practically unattacked 
(chloropicrin, chloroacetone, iodoacetone, etc.). 

Chlorovinyl dichloroarsine is rapidly hydrolysed by water. 
According to Vedder 1 this substance, though powerfully toxic, 
could not be efficiently used in open country because of its high 
velocity of hydrolysis. 

In general, oxygen-containing compounds are more stable than 
the corresponding sulphur-containing ones, according to Meyer, 2 
who adds that the stability increases with an increase in the length 
of a chain of carbon atoms. 

With respect to their employment in war a knowledge of the 
behaviour of substances towards water is of great importance, 
particularly by rendering it possible to define the conditions of 
humidity in which a certain substance may be employed, 
especially in considering the length of time during which it is 
desired to maintain an area in the gassed condition. 

The sensitivity to water seriously complicates both the storage 
of war gases and their filling into projectiles. Those which are 
readily hydrolysed need the employment of special precautions 
when they come into contact with air, which always contains 
water vapour, and when they are being filled into projectiles or 
storage containers, which must be quite dry internally. 

War gases must further possess a certain indifference towards 
the common chemical agents, as alkalies, acids, oxidants, etc. 
Chemical resistance contributes greatly to the aggressive value 
of a gas by making its destruction difficult. 

2. Stability on Storage 

Another type of stability required of a war gas is that it shall 
not undergo decomposition or polymerisation during storage. 
The decomposition which takes place in some substances, such as 
bromoacetone, hydrocyanic acid, etc., may be so inconvenient 
that the storage of such compounds is impossible. 

Polymerisation usually results in the formation of substances 
of little or no toxicity, as happens, for example, in the case of 
acrolein. 

This form of alteration has raised the problem of stabilisers, 
that is, substances which when added in quite small quantity, 
preserve the aggressive properties of the gas. For some of these 
gases, as acrolein, hydrocyanic acid, etc., efficient stabilisers are 

1 Vedder, Medical Aspects of Chemical Warfare, Baltimore, 1925, 158. 

2 Meyer, Der Gaskampf u. die chemischen Kampfstoffe, Leipzig, 1938, 72. 



14 PRINCIPAL PROPERTIES OF THE WAR GASES 



known, while for others the problem is still being studied, and at 
present it is still impracticable to employ some substances which 
in other ways present great interest as potential war gases. 

3. Stability to Explosion 

From the tactical point of view a substance which is to be 
employed in projectiles must be stable to the heat and pressure 
generated by the explosion of the bursting charge. With regard 
to the stability to heating, the substance must be able to resist the 
rise in temperature resulting from the explosion of the charge in 
the projectile. This is of great importance and limits the number 
of useful war gases. Among the substances hitherto considered, 
bromobenzyl cyanide shows some sensitivity to a rise in tempera- 
ture. Many others, including diphenyl chloroarsine, chloroaceto- 
phenone, etc., resist even high temperatures fairly well, while 
some, as chloropicrin, trichloromethyl chloroformate, etc., though 
decomposing with heat, have the advantage of producing equally 
toxic compounds in doing so. 

With regard to the resistance to the explosion pressure the 
insensitivity of war gases is another condition essential to their 
use in projectiles. Chloroacetophenone is practically completely 
insensitive. 

4. Absence of Attack on Metals 

The last requisite of a war gas is comparatively important : 
the absence of any attack on the material in which it is to be 
stored or used. Some war gases strongly attack the iron which 
commonly forms the storage containers and projectiles ; such 
are xylyl bromide, the incompletely chlorinated formates, 
bromobenzyl cyanide and a few others. 

This corrosive action necessitates the employment of special 
expedients, such as : 

(a) Protection of the metal walls of the container with layers of a 
substance which is not attacked, such as shellac, enamel, tin, etc. 

(b) Employment of a supplementary container which isolates 
the war gas from the walls of the container. (Containers of glass, 
lead, etc., are used.) 



CHAPTER II 



RELATION BETWEEN CHEMICAL STRUCTURE 
AND AGGRESSIVE ACTION 

The employment of toxic substances as a military arm has 
added interest to the study of the relation between physio- 
pathological action and chemical constitution, which started some 
years ago. 

This study, particularly important in the case of the war gases 
because of the guidance afforded in the discovery of new gases, 
has centred around the relation between their chemical structure 
and the type of action which they exert (lachrymatory, asphyxiant, 
sternutatory, etc.). 

The problem has always attracted intensive study and experi- 
ment, but owing to the short period during which this has been 
prosecuted, as well as the secrecy which has surrounded the 
results, it is not yet possible to state the general laws with any 
certainty. However, it will be of interest to give an account of 
the observations and hypotheses published on the influence of 
the structure of these substances, and in particular of the 
introduction of certain atoms or radicles, on the nature of the 
action exerted. 

The majority of the substances employed as war gases during 
the war of 1914-18 were organic. Among the inorganic compounds 
employed were chlorine, bromine, arsenic trichloride, etc. These, 
though having relatively little aggressive power, were used at 
the commencement of gas warfare chiefly because of the ease of 
their manufacture and the simplicity of their application. Various 
other inorganic substances, such as phosphine, arsine and stibine, 
although very toxic, have not been used as war gases because of 
their unsuitable physical properties. 

The organic compounds having aggressive action usually 
contain atoms of halogen, sulphur or arsenic or radicles such as 
— N0 2 , — CN, etc., in their molecules. It is to these atoms or 
radicles as well as to the molecular structure that the physio- 
pathological action is nowadays attributed. 

1. Influence of Halogen Atoms 

The halogens themselves have a noxious action on the animal 
organism and this diminishes in intensity in passing from fluorine 

13 



16 CHEMICAL STRUCTURE AND AGGRESSIVE ACTION 



to iodine, that is, it is less the greater the atomic weight of the 
halogen ; the tendency to combine with hydrogen also diminishes 
with increase in atomic weight. 

The introduction of halogen into the molecule confers aggressive 
properties which vary according to the nature of the halogen and 
the number of halogen atoms introduced. With regard to the 
influence of the nature of the halogen, it has been observed that 
the lachrymatory power of halogenated substances increases 
with increase of the atomic weight of the halogen present. 
Thus, bromoacetone is a more powerful lachrymatory than 
chloroacetone : 

Br — CH 2 — CO — CH 3 Lower limit of irritation i mgm./cu. m. 
C1-CH 2 — CO-CH3 18 

Benzyl iodide has a lachrymatory action superior to that of 
the bromide : 

C 6 H 3 — CH 2 I Lower limit of irritation 2 mgm./cu. m. 
C 6 H S — CH 2 Br „ „ ..4 » 
However, the truly toxic action varies inversely as the atomic 
weight of the halogen. Bromoacetone is less toxic than 
chloroacetone 1 : 

Br — CH 2 — CO — CH 3 Mortality-product 4,000 
CI— CH 2 — CO— CH 3 „ " „ 3,000 

Dibromoethyl sulphide is less toxic than dichloroethyl sulphide : 

/CH 2 CH 2 Br /CH 2 CH 2 C1 
S< 2 S< 

CH 2 CH 2 Br N CH 2 CH 2 C1 

Mortality-product 10,000 Mortality-product 1,500 

In considering the influence of the number of halogen atoms 
present it is found that while one halogen atom confers pre- 
dominantly lachrymatory properties on the molecule, an increase 
in the number of the halogen atoms diminishes the lachrymatory 
but increases the asphyxiant action. A typical example of this 
observation is the series of halogenated esters of formic acid. In 
this the first member, monochloromethyl chloroformate, has a 
predominantly lachrymatory action, while the last, trichloro- 
methyl chloroformate, has an essentially asphyxiant action and 
practically no lachrymatory property. 

ri rnnrw ri J Lower limit of irritation 2 mgm./cu. m. 
u— ^uul,h 2 li 1 Limit Qf jnsupportability 50 

ri morn / Lower limit of irritation 5 mgm./cu. m. 
w tWLLia \ Limit of insupportability 40 

1 The mortality products quoted in this chapter are those of German authorities 
{cp.-p. 4). 



INFLUENCE OF CHLORINE AND SULPHUR ATOMS 17 



Other examples occur in the series of chlorinated nitromethanes, 
in which it is found that the dichloro-derivative is less toxic than 
the trichloro-compound. 

This law is not, however, always applicable. With some 
substances, as dichloroethyl sulphide, diphenyl chloroarsine, etc., 
it is found that the introduction of further halogen atoms first 
diminishes and then destroys the aggressive properties of the 
original compound. 

The position occupied by the halogens in the molecule also has 
a notable influence on the aggressive properties. In the aliphatic 
series, it is found that compounds with the halogen atom in the /? 
position, 

CH 3 — CO — CH 2 — CH 2 C1 and CI— CH 2 — CH 2 — CO— O.C 2 H 5 
/3 chloroethyl methyl ketone and ethyl /3 chloropropionate 

are more powerful lachrymatories than their isomers which have 
the halogen in the a position, 

CH 3 — CO — CHC1 — CH 3 and CH 3 — CHC1 — CO — OC 2 H 5 
a chloroethyl methyl ketone and ethyl a chloropropionate 

In the aromatic series it is observed that the introduction of a 
halogen atom into the side chain of a substance confers lachryma- 
tory properties, while if it replaces a hydrogen atom from the 
benzene nucleus, a substance results which has no physiopatho- 
logical properties. Thus, from toluene, benzyl bromide, 
C 6 H 5 — CH 2 Br, is obtained in the first case. This has energetic 
lachrymatory properties, while bromotoluene, C 6 H 4 Br — CH 3 , has 
no toxic action. 

This difference in physiopathological properties is probably 
connected with a difference in the mobility of the halogen atom. 
It is noteworthy that if this is in the nucleus it is less easily 
removed than if it is in the side chain. 

The degree of mobility of the halogen atom has a great influence 
on the aggressivity of the substance. The halogen must not be 
bound in too labile a manner to the molecule, otherwise it will be 
attacked by atmospheric agencies or by the surface of the 
organism before the entire molecule has penetrated the cells. 
Neither may it be bound to the molecule in too stable a manner, 
otherwise the substance will be practically inert, for the atom 
will not even be detached in the interior of the organism. 

2. Influence of the Sulphur Atom 

Sulphur is not generally considered as a toxic element in the 
same way as are the halogens. Nevertheless, its presence seems 
to confer on a substance the capability of penetrating the 



18 CHEMICAL STRUCTURE AND AGGRESSIVE ACTION 

epidermis, which explains the actual aggressive properties of such 
compounds. 

An example of this observation is found in a comparison of 
substances containing a sulphur atom with their analogues 
which contain oxygen. For example, dichloroethyl sulphide 



no such properties. 

Comparatively few war gases contain sulphur in their molecules. 
It is generally observed that the degree of toxicity of the sulphur 
compounds varies with the valency of the sulphur atom and with 
the nature of the radicles with which the sulphur is united. 
Among the sulphur compounds those of the type R 2 S (divalent 
sulphur) are more toxic than those of the type R 2 SO (tetravalent 
sulphur) and far more than those of the type R 2 S0 2 (hexavalent 
sulphur). That is, the higher the valency of the sulphur atom, 
the lower the toxicity of the substance. Some studies have been 
carried out showing the relation between the decrease in toxicity 
observed when the sulphur atom in the molecule passes from the 
divalent to the hexavalent state, and the variation in physical 
properties, more especially the diminished solubility in lipoids. 
Those compounds in which the sulphur has a specific function 
also contain halogen atoms. Such are, for instance, dichloroethyl 
sulphide, dibromoethyl sulphide, etc. 

Little is known regarding the influence on the aggressive 
properties of a substance of the introduction of a sulphur atom. 
In the particular case of the derivatives of dichloroethyl sulphide, 
it has been observed that an increase in the number of sulphur 
atoms in the molecule does not notably diminish the vesicatory 



vesicatory power only one-third less than that of dichloroethyl 
sulphide. 1 

3. Influence of the Arsenic Atom 

The arsenic atom also imparts toxic properties to a higher 
degree than the sulphur atom. It is a general rule that substances 
containing a trivalent arsenic atom have a considerably greater 




properties. Dichloroethyl disulphide, e.g., | 



S-CH 2 -CH 2 CI 
I 

S-CH S -CH 2 CI 



has a 



1 Bennett, /. Chem. Soc, 1921, 119, 418. 



INFLUENCE OF THE ARSENIC ATOM 19 



physiopathological action than those containing a pentavalent 
arsenic atom. 

The arsenical war gases contain halogen atoms or organic 
radicles such as — CN, — SCN, etc., besides the arsenic atom. 
The nature of the aggressive action depends on the number 
and the nature of the organic radicles with which the arsenic 
atom is linked. 

In general, arsenical compounds have an aggressive action 
when two of the three valences of the arsenic atom are linked to 
like atoms or groups and the third to a different atom or radicle. 
If all the three valences of the arsenic atom are linked to similar 
atoms or radicles the compound has practically no aggressive 
action. Thus in the series of chlorovinyl arsines, it has been 
found that trichlorovinyl arsine has practically no aggressive 
action compared with chlorovinylchloroarsine or dichlorovinyl 
chloroarsine : 

,,CH=CHC1 /CH=CHC1 /CH=CHC1 

Asf CH=CHC1 Asf CI Asf CH=CHCL 

\CH=CHC1 X C1 \C1 

trichlorovinyl chlorovinyl dichlorovinyl 

arsine dichloroarsine chloroarsine 

In the series of aromatic arsines there is a great difference in 
aggressive action between triphenyl arsine, phenyl dichloroarsine 
and diphenyl chloroarsine. 

/C 6 H 5 7 C 6 H S /C 6 H 5 

Asf C 6 H 5 Asf CI Asf C 6 H 5 

\C 6 H 5 \ C 1 \C1 

triphenyl phenyl diphenyl 

arsine dichloroarsine chloroarsine 

In particular it may be observed that : 

(a) When the arsenic atom is linked to an unsaturated radicle, 
the substance has a predominantly vesicatory action, as in the vinyl 
chloroarsines, the styryl chloroarsines, etc. This physiopathological 
action decreases with increase in the number of organic radicles 
linked to the arsenic atom. Thus, substances with a single organic 
radicle have a more powerful vesicatory action than those with 
two or more organic radicles. A typical example of this observa- 
tion is found in the chlorovinyl arsine series, for chlorovinyl 
dichloroarsine has a greater vesicatory action than dichlorovinyl 
chloroarsine. 

(b) When the arsenic atom is linked to an alkyl or phenyl 
group, substances with a predominantly irritant action are 
obtained. This physiopathological action is accentuated in 



20 CHEMICAL STRUCTURE AND A GGRESSIVE ACTION 



compounds containing two such radicles linked to the arsenic 
atom : 

(C 6 H 6 ) 2 AsCl Diphenyl chloroarsine : Limit of insupportability, 
i mgm./cu. m. 

C 6 H 5 AsCl 2 Phenyl dichloroarsine : Limit of insupportability, 
16 mgm./cu. m. 

and in compounds containing the phenyl radicle rather than an 
alkyl radicle : 

C 6 H 5 AsCl 2 Phenyl dichloroarsine: Limit of insupportability, 
16 mgm./cu. m. 

CH 3 AsCl 2 Methyl dichloroarsine : Limit of insupportability, 
25 mgm./cu. m. 

(c) Arsenic compounds containing ethyl radicles are more toxic 
than the corresponding compounds containing methyl radicles. 
Thus the derivatives of ethyl arsine (the oxide, chloride, etc.) 
have a greater toxic action than the corresponding compounds 
of methyl arsine : 

C 2 H 5 AsCl 2 Ethyl dichloroarsine : Limit of insupportability, 
10 mgm./cu. m. 

CH 3 AsCl 2 Methyl dichloroarsine : Limit of insupportability, 
25 mgm./cu. m. 

(d) The substitution of the phenyl radicle by one of its higher 
homologues reduces the aggressive action of the resulting 
compound. For example, ditolyl chloroarsine is less irritant in 
its action than diphenyl chloroarsine. 

The presence of halogen atoms in the molecules of organic 
arsenicals usually confers irritant properties. Among these 
halogen compounds, those containing chlorine have a superior 
irritant power to the analogous bromine and iodine compounds, 
e.g., diphenyl chloroarsine has a greater irritant power than 
diphenyl iodoarsine. 

An increase in toxic power is also found in organic compounds 
whose molecules contain a cyanide radicle ; thus diphenyl 
cyanoarsine is more irritant than diphenyl chloroarsine : 

(C 6 H 6 )2AsCN Limit of insupportability, 0-25 mgm./cu. m. 
(CeHJ^sCl 

4. Influence of the Nitro Group 

The aggressive properties conferred on a substance by the 
introduction of the — N0 2 group depend on whether the group 
combines through an oxygen or a carbon atom, that is, whether 



INFLUENCE OF THE N0 Z AND CN GROUPS 21 



a nitrate or a nitro compound is produced. The nitrates have 
not been used as war gases, but very efficient agents are included 
among the nitro derivatives, e.g., trichloro nitromethane 
(chloropicrin), tribromo nitromethane, etc. 

In particular the introduction of the N0 2 group confers 
lachrymatory properties or increases any such tendency if it is 
originally present in the molecule. 

Typical examples of this are found among the nitro derivatives 
of the benzene halides : o-nitro benzyl chloride has a much more 
powerful lachrymatory action than benzyl chloride or than the 
corresponding bromide or iodide. 

C 6 H 5 CH 2 C1 Benzyl chloride : Lower limit of irritation, 77 

mgm./cu. m. 

C 6 H 5 CH 2 Br Benzyl bromide: Lower limit of irritation, 4 
mgm./cu. m. 

CgH^NOgjCHjjCl o-Nitro benzyl chloride : Lower limit of irrita- 
tion, i-8 mgm./cu. m. 

With an increase in the number of N0 2 groups the augmentation 
of the lachrymatory properties is sometimes found to be very 
great. Such is the case with tetrachloro dinitroethane, which is 
eight times as powerful a lachrymator as trichloro nitromethane. 

According to Nekrassov, and Hackmann, 1 the introduction of 
the N0 2 group into the molecule of an aromatic compound 
confers vesicatory properties, or increases any which the substance 
already possesses. 

The influence of the NOH group on the toxic properties of 
substances has only recently been studied, derivatives of carbonyl 
chloride such as dichloro- and dibromo-formoxime being examined. 
It seems that the NOH group causes accentuation of aggressive 
properties, in particular conferring " orticant " action (i.e., 
causing skin irritation). 

5. Influence of the — CN Croup 

To the CN group two different structures are attributed : one, 
— C=N, the nitrile, the other — N = C, the isonitrile grouping. 
It has been observed that compounds containing the isonitrile 
group have more powerful toxic properties than those containing 
the nitrile. This difference in biological properties can be 
compared with the greater facility with which compounds 
containing the isonitrile radicle liberate hydrocyanic acid. 

The presence of a second CN group generally diminishes the 
aggressive properties of a substance, and the presence in the 

1 Nekrassov, Khimija Otravliajuscik Vescestv, Leningrad, 1929 ; and 
Hackmann, Chem. Weekblad, 1934, 31, 366. 



22 CHEMICAL STRUCTURE AND AGGRESSIVE ACTION 



same molecule of the — CN group and of other atoms such as 
halogens, while reducing the toxic action of the substance, 
confers highly lachrymatory properties. For example, cyanogen 
bromide and iodide are much less toxic than hydrocyanic acid 
but are powerful lachrymators. The same rule applies in the 
case of such aromatic derivatives as bromobenzyl cyanide, 
chlorobenzyl cyanide, etc. 

6. Influence of Molecular Structure 

According to various observations, the aggressive action of a 
substance depends not only on the presence of particular atoms 
or radicles in the molecule, but also on the molecular structure, 
and in particular on 

(a) The presence of unsaturated bonds, and 

(b) The molecular symmetry. 

Influence of Unsaturated Bonds. The presence of unsaturated 
bonds in the molecule usually involves an increase in the 
physiopathological properties. This observation was made by 
Loew in 1893. 

Among the war gases various examples occur of the influence 
of the unsaturated bond. Thus, acrolein CH 2 = CH — CHO, 
has strongly irritant properties, while the corresponding saturated 
aldehyde, propionaldehyde, CH 3 — CH 2 — CHO is innocuous. 
Similarly, /? chlorovinyl dichloroarsine, CI — CH = CH — AsCl 2 , is 
a powerful vesicant, while the corresponding saturated compound, 
/? chloroethyl dichloroarsine, CI — CH 2 — CH 2 — AsCl 2 , has only weak 
vesicatory properties. 1 

Other examples may be found among the mono- and di- 
halogenated acetylenes, such as diiodo- and dibromo-acetylene, 
CI 2 = C and CBr 2 = C, which have more interesting 
physiopathological properties than the halogenated paraffin 
hydrocarbons. 

Influence of Molecular Symmetry. The spatial arrangement of 
the functional groups in a molecule has a definite influence on 
the degree of its toxicity. It has been observed that substances 
with symmetrical molecules generally have a more powerful 
aggressive action than asymmetrical substances. Thus, 
symmetrical-dichloroacetone, 




CH 2 -C1 



1 Ferrarolo, Minerva Medica, 1935, 27, II, 30. 



GENERAL THEORIES : MEYER'S THEORY 23 



has great irritant powers, while asymmetrical dichloroacetone 

CH 3 
I 

CO 

CHCV 

is almost completely lacking in irritant properties. 

Another example occurs in the series of halogenated methyl 
ethers. When the halogens occupy a symmetrical position, as 

/CH 2 -C1 

in sym. dichloromethyl ether, Oy the substance has a 

CH 2 — CI 

much more energetic lachrymatory action than that in which 
the chlorine atoms are asymmetrically placed, i.e., in asyrn. 

/CH 3 

dichloromethyl ether 0\ 

N CH-C1 2 

7. Theories of General Nature 

General theories concerning the relation between chemical 
structure and physiopathological action have been elaborated 
with especial reference to the war gases. From among the many 
published, an account is given here of two : Meyer's Theory and 
the " Toxophor-Auxotox " Theory. 

Meyer's Theory. According to this theory, 1 the physio- 
pathological action of war gases is attributed to certain atoms or 
radicles which have a tendency to react easily with other 
substances by addition. This classification on the basis of their 
ease of reaction should be determined by their combination with 
the various biological entities or tissues (as the blood, the nerve 
cells, the respiratory epithelia, etc.) which undergo specific and 
characteristic alterations. 

To one group belong, for example, the halogen atoms, as the 
chlorine in phosgene, cyanogen chloride and the chlorovinyl 
chloroarsines ; the bromine in ethyl bromoacetate, cyanogen 
bromide, etc. These atoms are linked in a very labile manner 
to the remainder of the molecule and react easily with water and 
other substances. Also the oxygen atom is highly reactive when 
in the vicinity of a halogen in the halogenated aldehydes, esters 
and ethers, such as dichloromethyl ether, trichloromethyl chloro- 
formate, etc. 

The radicles which react most easily are the N0 2 — group in 
0- nitro benzyl chloride and bromide, the CO — group in the 

1 J. Meyer, Der Gaskampf u. die chemischen Kampfstoffe, Leipzig, 1926, 90. 



24 CHEMICAL STRUCTURE AND AGGRESSIVE ACTION 



halogenated ketones and the CN — group in bromobenzyl cyanide 
and diphenyl cyanoarsine, etc. All these radicles, which are 
notable for their reactivity with water or other substances, 
confer a certain degree of toxicity by their presence in the 
molecule. However, on considering the structure of the molecules 
of the war gases, it is seen that while some of these contain atoms 
or radicles of great reactivity, others are distinguished by an 
unusual resistance to chemical reagents yet possess a high degree 
of aggressiveness. 

In such cases, Meyer suggests, the aggressive action may be 
attributed to the capacity of the entire molecule of forming 
additive compounds with vital constituents of the organism. 

Toxophor-Auxotox Theory. The theory of toxophors and 
auxotoxes, first elaborated by Ehrlich 1 for toxic substances and 
later applied by Nekrassov 2 to the war gases, attributes the 
physiopathological properties of these substances to special 
atoms or radicles in a similar manner to Witt's theory regarding 
the colour of organic substances. 

Witt's theory of coloured substances may be summarised as 
follows : the presence of colour in a substance depends on the 
presence of certain atomic groupings called " chromophores." 
For instance, the — N = N — group characteristic of the azoic 
colours, the — N0 2 group, the = C = O group, etc. It is to the 
presence of these groups that the more or less intense colouration 
of a compound is due. But in order that a coloured substance 
may be capable of being fixed on animal or vegetable fibres, it 
must have in the molecule not only chromophoric groups, but also 
contain other groups, called " auxochromes " which give it the 
capability of combining intimately with the fibre. Typical 
auxochromic groups are : NH 2 , OH, etc. 

The war gases, according to Nekrassov, have structures 
analogous to those of coloured substances. By examining the 
chemical structures of the war gases, certain atomic groups are 
found which confer on substances the potentiality of becoming 
war gases, in the same way as Witt found certain groupings 
common to coloured substances. The groupings found in war 
gases are called " toxophors." Such are, for example : 

>CO ; S< ; >C=C< ; - N \ Q : -N«C ; -As< ; etc. 

There also exist other groups capable of communicating the 
characteristic toxic functions of the toxophoric group, that is, of 

1 P. Ehrlich, Deut. med. Wochschr., 1898, 1052. 

2 Nekrassov, Khimija Otravliajuscikh Vescestv, Leningrad, 1929, 30 



THE TOXOPHOR- AUXOTOX THEORY 25 



transforming into actuality the latent capacity of the toxophor 
group. These groups are named " auxotoxes," and may be 
either : 

atoms : halogens, oxygen, etc. 

or 

atomic groups : — NH 2 , benzyl, phenyl, methyl, ethyl 
radicles, etc. 

With the aid of this theory it is explained that just as in 
coloured substances the introduction of some auxochromic 
groups changes the colour of the substances, so in the war gases 
the presence of certain autotoxes can alter the type of biological 
action. Thus, for example, halogen introduced into the 
hydrocyanic acid molecule reduces the toxicity of the toxophor, 
— CN, and confers on the product lachrymatory properties. 

Also, the auxotoxic groups in the war gases, like the auxo- 
chromes in coloured substances, differ in their effect according 
to their positions in the molecules. Thus the halogens differ in 
their influence according to whether they are in a methyl or an 
ethyl group, at the end or the beginning of a side-chain. It is 
easily seen that a halogen atom distant from the end of a side-chain 
has little influence on the aggressive power. 

/CHBr-CHo 
CO< 
X CH 3 

a bromoethyl methyl ketone is less lachrymatory in action than 

/CH 2 — CH 2 Br 
X CH 3 

/? bromoethyl methyl ketone. 

/CHCI-CH3 

Similarly, oca' dichloroethyl sulphide S< has only 

N CHC1-CH 3 

slight aggressive power, while /?/?' dichloroethyl sulphide (mustard 
/CH 2 -CH 2 C1 

gas) S( has an aggressive action which is well known. 

CH 2 — CH 2 C1 

However, Nekrassov's theory cannot be applied so generally 
to the war gases as Witt's to coloured substances. 

In some cases there are actually strongly marked differences. 
Thus in the coloured substances the auxochrome group brings 
out the latent colour-potentiality of the chromophore group and 
so makes colouration possible, while in the war gases the auxotox 
group merely develops the characteristic property of the toxophor 



co( C 



26 CHEMICAL STRUCTURE AND AGGRESSIVE ACTION 



group. On the other hand, the merest glance at the chemical 
structures of the war gases will show that the auxo group may 
function either positively or negatively. That is, on its presence 
depends the increase or the decrease, or sometimes even the 
destruction of the toxicity of the substance (e.g., the introduction 
of alcoholic, sulphonic groups, etc.). 

In coloured substances, increase in molecular complexity leads 
not to a decrease of the colour, but to its strengthening, while it is 
observed that an increase in the number of toxophors or auxotoxes 
in the molecule does not increase the toxicity. Typical is the case 
of j8j8' dichloroethyl sulphide in which the introduction of more 
chlorine atoms into the molecule produces the tetra- and 
hexachloro- compounds whose aggressive action is practically nil. 

Furthermore, this theory, like that of Meyer already described, 
though having many interesting aspects, does not sufficiently 
explain the behaviour of some of the war gases. 

Many gaps still exist in this field of study. The many 
discussions and the various theories put forward show merely 
the efforts which have been made to solve this important problem. 

It must be concluded that only after a long series of studies 
and experiments will it be possible to enunciate general and 
precise laws on the relation between chemical constitution and 
the aggressive action of the war gases. These laws, besides 
supplying a profound knowledge of the science of war gases, will 
be invaluable in preparing new substances of greater value in 
warfare. 



CHAPTER III 



CLASSIFICATION OF THE WAR GASES 

The classification of the war gases is particularly difficult 
because of the many aspects which these substances, some 
similar to one another, some completely different, present. The 
number of methods of classification which have been proposed 
are an indication of this difficulty. 

Without entering into unnecessary detail, a few of the more 
important classifications in use at present will be given, with 
especial emphasis on the chemical nature of the gases. 

1. Physical Classification 

The physical classification of the war gases has often been 
proposed by taking as criterion either their state of aggregation, 
or their boiling point. 

The method of classification most used to-day is based on their 
state of aggregation at ordinary temperatures. According to this 
classification the war gases are divided as follows into three 
groups : 

Gaseous. Chlorine, phosgene, etc. 

Liquid. Bromine, chloropicrin, dichloroethyl sulphide (mustard 
gas), etc. 

Solid. Diphenyl chloroarsine, diphenyl cyanoarsine, 
chloroacetophenone, etc. 

This classification is altogether too crude, uniting in one and 
the same group very varied substances which have only a single 
quality in common — one which is not generally considered to be 
the most important. Moreover, the one criterion of the classifica- 
tion is influenced by temperature, so that by normal temperature 
changes of the air a substance may pass from one group to the 
other, for example, dichloroethyl sulphide from liquid to solid, 
phosgene from gas to liquid. 

2. Tactical Classification 

This classification is based on the criterion of the tactical 
employment of the war gases. From this view-point they are 
divided into two groups : 

27 



28 CLASSIFICATION OF THE WAR GASES 



Non-persistent Gases. Including substances which diffuse into 
the air in a short time, losing some of their toxic concentration : 
chlorine, phosgene, hydrocyanic acid, etc. 

Persistent Gases. Including substances which vaporise only 
slowly and remain on the ground for long periods in the liquid or 
solid state, still retaining their aggressive power : dichloroethyl 
sulphide, etc. 

This classification also lacks neatness and precision, for the 
place of some substances in it is doubtful. It is proposed 
nowadays to add a third intermediate group, to include substances 
whose vapour tension lies between the gases of the first group 
and those of the second. This third group has been termed that 
of the " Semi-persistent Gases." 

Another tactical classification which may be mentioned is one 
largely employed in text-books on chemical warfare and was in 
use in Germany during the war. In this classification the gases 
are divided into the following four classes : 

Green Cross Gases. This includes substances with a high 
vapour tension and great toxic power on the respiratory tract : 
phosgene, trichloromethyl chloroformate (diphosgene), chloro- 
picrin, etc. 

Yellow Cross Gases. This includes substances with a low vapour 
tension and high toxic and vesicatory power : dichloroethyl 
sulphide (mustard gas), chloro vinyl dichloroarsine (lewisite), etc. 

Blue Cross Gases. This includes solid substances with low 
volatility and great irritant power : diphenyl chloroarsine, 
diphenyl cyanoarsine, etc. 

White Cross Gases. This includes the powerful lachrymators : 
bromoacetone, chloroacetophenone, etc. 

3. Physiopathological Classification 

This classification is based on the most characteristic action of 
each war gas on the living organism. Various classifications 
have been made on this basis (German, English, American, etc.). 
The usual method is to divide the gases into the following 
classes : 

(A) The Toxic Suffocants (or Lung Irritants). These 
include those gases which act principally on the respiratory 
tract : chlorine, phosgene, chloropicrin, etc. 

(B) The Vesicants. These include those substances whose 
characteristic action is to produce blisters on the skin : 
dichloroethyl sulphide, chlorovinyl dichloroarsine, etc. 

(C) The Irritants. These include substances having lachryma- 



BIOLOGICAL AND CHEMICAL CLASSIFICATIONS 29 



tory power : benzyl chloride and bromide, and those causing 
sneezing (the sternutatories) : diphenyl chloroarsine, etc. 

(D) The Toxic Gases. These include those gases acting 
particularly on the blood, as carbon monoxide, or on the nervous 
system, like hydrocyanic acid, etc. 

The physiopathological classification of the war gases, though 
used very widely, is even less exact than the others mentioned. 
In point of fact the biological action of these substances is 
extremely complex and in certain concentrations a gas may 
change its action to that of another group. 

In order to classify these substances accurately on this basis 
the new tendency to-day is to regroup them according to the 
actual mechanism of their action on the human organism. In 
this,, however, there is still so much work to be done that 
with regard to a great many substances practically nothing 
is known. 

4. Chemical Classification 

Classification of the war gases according to the characteristic 
chemical groups in their molecules has been almost completely 
neglected. It is only by taking the chemical characteristics of 
the substances as the sole criterion that it will be possible to 
elaborate a precise and complete classification of the war gases, 
and these chemical characteristics must be quite definite both 
as to the nature and the number of atoms in the molecule. 

The first attempts at a chemical classification of the war gases 
were those of Chugaev 1 in 1918 and of Zitovic. 2 These classifica- 
tions are, however, merely schematic and are particularly lacking 
in precise and distinctive characteristics. 

Later, other chemical classifications were proposed, and two 
of these will be outlined here — that of Jankovsky and that of 
Engel. 

(a) Jankovsky's Classification. In 1925 Jankovsky 3 proposed 
a completely new classification, founding it on a study, then in its 
infancy, of the relationship between the chemical constitution and 
the aggressive action of the war gases. It was based on the theory 
of toxophoric and auxotoxic groups which has been described in 
the preceding chapter. In this classification the war gases are 
grouped according to the toxophoric group present in their 
molecules, being divided in this way into the following six 
classes : 

1 Chugaev, Khimiceshi Osnovi gas i protivogas diela, 191 8. 

2 Zitovic, Khimiceskaja Promisclennost, 1924, 11, 295. 

3 Jankovsky, Voina i Tecnica, 1925, nn. 220-221, 23. 



3« 



CLASSIFICATION OF THE WAR GASES 



Class I 

Toxophoric Group. Chlorine, bromine, iodine, etc 
Auxotoxic Group. Phenyl, benzyl, etc 



Includes : Benzyl chloride 

Benzyl bromide . 
Benzyl iodide 
o-Nitrobenzyl chloride 
Dichloromethyl ether 
Dibromomethyl ether 

Class II 



C 6 H 5 — CH 2 C1 
C 6 H 5 -CH 2 Br 
C 6 H 5 — CH 2 I 
C 6 H 4 — (N0 2 )CH 2 C1 
C1CH 2 — 0— CH 2 C1 
BrCH 2 — 0 — CH 2 Br 



Group. Unsaturated oxides. 

Includes : Carbon monoxide . . CO 
Sulphur dioxide . . . S0 2 
Nitrogen oxides . . . NO ; N0 2 ; N 2 0 3 

Class III 
Toxophoric Group. CO. 

Auxotoxic Group. Halogens, or double bonds. 

. CH 3 — CO— CH 2 C1 



Includes : Chloroacetone 
Bromoacetone 
Bromomethyl ethyl ketone 
Chloroacetophenone 
Ethyl chloroacetate 
Phosgene 
Acrolein 

Class IV 
Toxophoric Group 
Auxotoxic Group. 
Includes : Perchloromethyl mercaptan 

Dichloroethyl sulphide . 

Dibromoethyl sulphide . 

Sulphoxides 

Sulphones . 

Esters of sulphuric acid 
Class V 

Toxophoric Group. — C^N ; — N = C ; — N0 2 . 
Auxotoxic Group. Halogens, benzyl, etc. 



CH 3 — CO— CH 2 Br 
C 2 H 8 — CO— CH 2 Br 
C 6 H 5 — CO— CH 2 C1 
C1CH 2 — COO— C 2 H 5 
C0C1 2 
. CH 2 =CH— CHO 

S; S = 0;0 = S = 0. 
Halogens, methyl, etc. 

CC1 3 — S— CI 
S(CH 2 — CH 2 — Cl) 2 
S(CH 2 — CH 2 — Br) 2 
0=SR 2 
0=SR 2 =0 
0=S(OR) 2 =0 



HCN 
CNC1 

C 6 H 5 — CH(CN)Br 



Includes : Hydrocyanic acid 
Cyanogen chloride 
Bromobenzyl cyanide . 
Chloropicrin 

Tetrachloro dinitroethane 

Class VI 

Toxophoric Group. — As =. 

Auxotoxic Group. Methyl, ethyl, vinyl, phenyl. 

Includes : Methyl dichloroarsine . . CH 3 AsCl 2 
Ethyl dichloroarsine . . C 2 H 5 AsCl 2 
Diphenyl chloroarsine . . (CgH^gAsCl 
Diphenyl cyanoarsine . . (CgHjjgAsCN 
Phenarsazine chloride . . NH(C 6 H 4 ) 2 AsCl 



CC1 3 — N0 2 
(CC1 2 -N0 2 ) 2 



Table XII 



GROUP 



Series 


I 


2 


3 


4 


5 


6 


7 


8 


Hydrocarbons 


Alcohols 


Ethers 


Aldehydes 
and Ketones 


Acids 


Esters 


Amines 


Arsines 


I 


CC1 3 N0 2 
Chloropicrin 




.CH„C1 

X CH 2 C1 
Dichloromethyl 
ether 




COCl 2 
Phosgene 

< 


CI— COOCClj 
Diphosgene 

>< 




CH S — AsCl 2 
Methyl 
dichloroarsine 


II 






yCH 2 CH 2 Cl 

\CH 2 CH a Cl 
Dichloroethyl 
sulphide 






CH 2 Br — COOC 2 H 5 
Ethyl 
bromoacetate 




C 2 H 5 — AsCl 2 

Ethyl 
dichloroarsine 

>r 


III 








/CHjBr 

CO< 
N CH 3 
Bromoacetone 










IV 


C 6 H 6 — CH 2 Br 
Benzyl 
bromide 






/CHjCl 
Chloroacetophenone 






C 6 H 5 N = CC1 2 
Phenyl 
carbylamine 
chloride 


(C„H 5 ) a AsCl 

Bjgbenyl 
chlorjfersine 



32 CLASSIFICATION OF THE WAR GASES 



(b) Engel's Classification. Another chemical classification of 
war gases is that proposed recently by Engel. 1 It is an improved 
version of that published by him in 1928, 2 and divides the war 
gases into eight groups (see Table XII). These correspond to 
eight of the simplest organic types of compounds, arranged 
according to their differing oxygen-content : hydrocarbons, 
alcohols, ethers, aldehydes and ketones, acids, esters, amines, 
arsines. The two last types — the amines and the arsines — may 
be considered as hydrocarbons in which a hydrogen atom is 
substituted by an NH 2 group or an AsH 2 group respectively. 

Each of these groups of substances may be sub-divided into 
four series : The first three of these comprise the aliphatic 
compounds derived from methane (series I), ethane (series II) 
and propane (series III) . The fourth series comprises the aromatic 
compounds derived from benzene and its homologues. 

All the war gases have not been included in Table XII, but 
only the most important. Those not included may be -easily 
classified into their proper groups. Acrolein, for instance, in the 
aldehyde group, lewisite and diphenyl cyanoarsine in that of the 
arsines, methyl cyanoformate and methyl chloroformate in that 
of the esters. 

According to Engel this classification allows for the allocation 
of gases which have never yet been employed in warfare. Stibine 
and phosphine, for example, may be considered as arsines in 
which the arsenic atom has been substituted by that of antimony 
or phosphorus ; similarly dichloroethyl selenide and telluride 
may be considered as ethers in which the oxygen atom has been 
replaced by that of selenium or tellurium. 

This and other classifications of war gases will not be considered 
further. 

It is possible to arrange the war gases in the chronological order 
in which they were first used in the war of 1914-18. This is the 
order employed in Table XIV at the end of this book, where the 
physical, chemical and physiopathological properties of the 
principal war gases are summarised. In the text, however, it is 
considered more convenient to catalogue them according to 
chemical relationships and similarity of structure. 

1 Engel, Gasschutz und Luftschutz, 1935, 239. 

2 Engel, Z. ges. Scheiss.-Sprengstoffw., 1928, 23, 321. 



PART II 



CHAPTER IV 

THE HALOGENS 
1. Chlorine. Cl f . (l1f.Wt.70-9) 

Chlorine may be considered as the only substance which has 
been used in the elementary state as a war gas. 

Its asphyxiating properties have been recognised ever since it 
was discovered in 1774 by Karl Wilhelm Scheele. 

Its use in war was due to its conforming to the principles of gas 
warfare : its ease of production, its low cost and also its high 
specific gravity, an important characteristic in the forcing of 
gases by the wind into the zone to be gassed. It is more useful 
than other agents for employment in wave-attacks. Later it 
lost much of its offensive importance, especially when very simple 
defensive means were found against it and when the method of 
wave-attack was replaced by the use of gas projectiles. However, 
this element still retains much interest as it forms the most 
important raw material for the preparation of other war gases. 

As the various methods of preparing this element are generally 
known and will be found in the inorganic chemistry text -books, 
it is considered unnecessary to spend time describing them here. 
Those physical and chemical properties which have considerable 
interest in chemical warfare will be considered instead. 

Physical and Chemical Properties 

Chlorine is a yellowish-green gas with an irritating and 
characteristic odour. 

Under normal conditions of temperature and pressure (0° C. 
and 760 mm.) a litre of chlorine weighs 3-22 gm., 1 and its density 
compared with that of air is therefore 2-49 (= 3-22 : 1-293). 
Because of this high density a cloud of chlorine rises slowly, 

1 At other temperatures and pressures, the weight of a litre of chlorine varies 
according to the Boyle-Gay-Lussac law. From the following formula the weight 
of 1 litre of any gas may be calculated at temperature t and pressure h, from a 
knowledge of the value at o° C. and 760 mm. : 

h x 273 

gr. = gr. X 

t&h o°&7 6 ° 7 6 ° ( 2 73 + ') 



WAR GASES. 



33 



3 



34 



THE HALOGENS 



clinging to the earth until an air current blows it away or 
dilutes it. 

Chlorine is fairly easily liquefiable ; at ordinary temperatures 
it can be liquefied by a pressure of 6-8 atmospheres, while at 
normal pressure it liquefies at — 40° C. 

The critical temperature of chlorine, i.e., the temperature 
above which it cannot be liquefied whatever pressure is 
applied, is 146° C. The critical pressure, i.e., the pressure 
necessary to liquefy chlorine at the critical temperature, is 
93-5 atmospheres. 

Liquid chlorine is green with a tinge of yellow and is very 
mobile. It boils at ordinary pressure at — 33-6° C. The value 
of the vapour tension of liquid chlorine at different temperatures 
is given in the following table : 



TEMPERATURE VAPOUR TENSION 

0 C. ATMOSPHERES 

— 20 i-8 

— IO 2-63 

o 3-66 

10 4-95 

20 6-62 

30 875 

40 ri-5 

100 417 



From this table it is seen that the pressure in a cylinder of 
liquid chlorine at 20° C. is 6-62 atmospheres. 

Liquid chlorine has a somewhat high coefficient of expansion : 
at 0° C. it is 0-00187 >' a * 2 °° C-> 0-00212, and at 50° C, 0-00259. 

From this it may be calculated that while 1 kg. of liquid 
chlorine at — 35° C. occupies 641-5 ml., at 60° C. it has a volume 
of 782 ml., that is, it increases 21-9% in volume. 

The specific gravity of liquid chlorine at various temperatures 
is as follows : 

TEMPERATURE 

0 C. S.G. 

- 35 I-5589 
o 1-4685 
20 1-4108 

30 1-3799 
60 1-2789 



One litre of liquid chlorine gives 463-8 litres of gaseous chlorine 
at 0° C. and 760 mm. The latent heat of vaporisation of liquid 
chlorine at 0° C. is 62-7 calories. 



CHLORINE : PROPERTIES 



35 



Chlorine on cooling to — 102° C. solidifies to a yellow crystalline 
solid. 

It is soluble in water ; at 760 mm. and the temperature stated, 
1 litre of water dissolves the following quantities of chlorine 1 : 



TEMPERATURE 
°C. 


ML. CHLORINE AT 
0° AND 760 MM. 


GM. CHLORINE 


IO 


3.095 


9-97 


15 


2.635 


8-48 


20 


2,260 


7-27 


25 


1.985 


6-39 


30 


1,769 


5-69 



The solution obtained has a yellowish-green colour and is 
termed chlorine water. By cooling this solution to — 8° C. a 
crystalline hydrate of the following composition 

C1 2 .8H 2 0 

separates ; on heating, it again decomposes. 

Chlorine also dissolves easily in carbon tetrachloride (at 13° C. 
to the extent of 10% by weight), in sulphuryl chloride, in 
tetrachloroethane and in pentachloroethane. 8 

Chemically, chlorine is one of the most active elements and 
combines directly with almost all simple bodies. 

It combines with hydrogen under the influence of light and 
heat, and reacts energetically with most of the non-metals 
forming the respective chlorides. By this method arsenic 
trichloride may be prepared and this is employed in the prepara- 
tion of the chlorovinyl arsines (Perkins's method) and diphenyl 
chloroarsine (Michaelis's method). Sulphur chloride is prepared 
similarly, and this is employed in the preparation of dichloroethyl 
sulphide by Guthrie's method. 

Chlorine combines also with almost all metals. Potassium 
placed in chlorine gas inflames with evolution of heat. Mercury 
combines at ordinary temperature. Chlorine has no action on 
other metals if it is perfectly dry, but reacts vigorously in the 
presence of moisture or on heating with sodium, calcium, 
magnesium, aluminium and tin (especially if finely divided), but 
only slowly with silver, gold and platinum. Among these 
compounds of chlorine with metals, aluminium trichloride is 

1 L. Winkler, Die Chemische Analyse, Vol. XXXV. (Ausgewdhlte Untersu- 
chungsverfahren fur das chemische Laboratorium) , Part II, 1936, p. 27. 
* Perkins, /. Chem. Soc, 1894, 65, 20. 

2—2 



36 



THE HALOGENS 



important for its use in the syntheses, in industry as well as in 
the laboratory, of many substances of application in war, as 
chloroacetophenone, the chlorovinyl arsines, etc. 

Chlorine can also combine directly with certain compounds, 
such as the addition to sulphur dioxide and to carbon monoxide 
to form sulphuryl chloride and carbonyl chloride (phosgene) 
respectively. The latter has wide application as a war gas. 

Other additive reactions take place with the unsaturated 
hydrocarbons, such as that with ethylene to form ethylene 
dichloride : 

C 2 H 4 + Cl 2 = C 2 H 4 C1 2 . 

Chlorine does not usually react in this manner however. 
More frequently the mode of reaction is of a different type. 
Thus with binary hydrogen compounds it reacts combining with 
the hydrogen and freeing the other element. For example, 
bromine and iodine are respectively liberated from hydrobromic 
and hydriodic acids. 

Water is also decomposed with liberation of oxygen : 
Cl a + HOH = 2HCI + 0. 

This reaction is reversible and arrives at a state of equilibrium. 
In this condition decomposition is very slow, becoming almost 
instantaneous, however, in the presence of easily oxidisable 
bodies. 

Chlorine reacts similarly with a large number of metallic 
oxides, forming the metal chloride and evolving oxygen. In 
presence of water and of soluble metallic oxides, oxygen is not 
formed, but unites with the chlorine to form salts of the 
oxygenated acids of chlorine (hypochlorites or chlorates). 

If chlorine is bubbled through a cold, dilute solution of an 
alkali hydroxide, chloride and hypochlorite are formed, as, for 
example, with sodium hydroxide : 

Cl 2 + 2NaOH = NaCIO + NaCl + H 2 0. 

This mixture is known as " Labarraque Water." The correspond- 
ing product obtained from potash is " Javel Water." With lime, 
however, there results a compound to which the following 
formula is generally given : 

/CI 
Ca< 

Ndci 

which is the familiar " chloride of lime." This compound is some- 
what unstable and has an oxidising and chlorinating action. 
Because of this property, chloride of lime is used as a disinfectant, 
and especially for the destruction of several of the war gases. 



BROMINE : PREPARATION 



37 



Chlorine irritates the respiratory tract in a concentration 1 of 
3-6 parts per million of air (= 10 mgm./ cu. m.). The limit of 
insupportability, i.e., the highest concentration which a normal 
man can breathe for 1 minute is 100 mgm. per cu. m. of air. 2 
Haber's product of mortality, or lethal index, i.e., the product of 
the concentration of chlorine in the inhaled air (expressed in 
mgm. per cu. m.) by the duration of its action (expressed in 
minutes) to cause the death of animals, is 7,500 for cats according 
to Flury, 3 and 56,000 for dogs according to Prentiss. 4 

2. Bromine. Br 2 . (M.Wt. 159 84) 

In the war of 1914-18 this element had a very limited use as a 
war gas. It was only used together with chlorine in order to 
increase the persistence of the latter, but according to some 
authorities 5 could be used alone if carried in special bombs. 

Bromine was discovered in 1826 by Balard, who extracted it 
from saline mother-liquors. It has since been obtained also from 
the ash of algae, but nowadays is obtained almost exclusively 
from the Stassfurt salt deposits and from saline mother-liquors. 

Preparation 

Only the more important methods of preparation of this 
element will be given. In the laboratory bromine may be 

1 Method of Expressing Concentrations. The following methods are in common 
use to express concentrations of gases and vapours in air : 

(a) Parts by volume. 

(6) Weight per volume of air. 

The expression as parts by volume, that is, parts per cent., per thousand, per 
hundred thousand or per million, is employed particularly in toxicology. Though 
often convenient, it forms a true basis of comparison of the toxicity of substances 
only when these have approximately equal molecular weights. 

Of more practical use for war gases is the expression of concentrations in weight 
of substance per unit volume of air, usually in mgm. per cu. m. 

To convert mgm. per cu. m. to parts per million, the following formula may be 
used : 

mgm./cu. m. x 22-4 ... .... 

—5 — ! 3 = ppm. (M = molecular weight) 

while to convert parts per million into mgm./cu. m., the following may be 
employed : 

ppm. x M , 

— • = mgm./cu. m. 

22-4 0 ' 

By means of Table XIII, at the end of this volume, values of concentrations 
in parts per million may be converted into mgm. per cu. m., and vice versa. 

2 U. Muller, Die Chemische Waffe, Berlin, 1932, 57. 

3 F. Flury, Z. ges. expt. Med., 1921, 13, and Gasschutz und Luftschutz, 1932, 
149. The values for mortality-products reported by Flury are considered as 
minimum values. 

* Prentiss, Chemicals in War, New York, 1937, l6 - 

6 Chlopin, Grundlagen des Gasschutzes. Extract in Z.ges. Schiess-Sprengstoffw,, 
1927 and 1928. 



38 



THE HALOGENS 



prepared by heating sodium bromide with sulphuric acid and 
manganese dioxide : 

2NaBr + Mn0 2 + 3H 2 S0 4 = MnS0 4 + 2NaHS0 4 + 2H 2 0 + Br 2 
But more usually it is preferable to purify commercial bromine 
for use. This is carried out by washing the bromine repeatedly 
with water, 1 then dissolving it in a concentrated solution of 
calcium bromide and reprecipitating it from this with excess of 
water. Bromine is thus obtained free from chlorine and may be 
dried over calcium bromide and oxide, shaken with phosphoric 
anhydride and then distilled in a current of carbon dioxide. 

Industrial Manufacture 

The bromine industry has grown considerably in recent years 
with the utilisation of that in the mother-liquors from the 
Stassfurt salts in Germany and of that in saline mother-liquors in 
America. 

The method used in Germany (Pfeiffer process) is based 
essentially on the following : 

The mother-liquors from washing the salts, in which bromine 
exists in the form of bromides, is sprayed in the form of a fine 
rain from the top of a tower filled with fragments of a refractory 
material, while into the bottom of the tower is led a current of 
chlorine and water vapour. By this means bromine is displaced 
from the bromide. The liquid which collects at the bottom of the 
tower is rich in bromine and passes into another vessel where it 
is distilled by means of superheated steam. The bromine which 
is vaporised passes from the top of the tower into a lead vessel 
where it is purified from the chlorine it contains by heating. 

In America bromine is obtained by treating the saline mother- 
liquors with dilute sulphuric acid and then adding to the previously 
concentrated liquid, manganese dioxide and sulphuric acid. The 
mixture is then distilled, when the bromine passes over together 
with water and a little bromine chloride. 

According to a recent American patent of the Dow Chemical Co. 
bromine is prepared by the electrolysis of saline mother-liquors ; 
by this means chlorine liberated in a nascent condition displaces 
the bromine which is recovered by a current of hot air. 

Physical and Chemical Properties 

Bromine is a heavy liquid of a dark red colour and an irritating 
and repugnant odour, from which it derives its name. 

It boils at 59 0 C. and has a specific gravity of 3-18 at 0°. Its 

1 B. Brauner, Monatsh., 1889, 10, 411. 



BROMINE : PROPERTIES 



39 



vapour also has a high specific gravity (about 5-5 times that of 
air) and is reddish-brown in colour. 

The vapour tension of bromine varies with temperature as 
follows (Landolt) : 

TEMPERATURE VAPOUR TENSION 

0 C. MM. MERCURY 

0-13 62 

4 77-3 
20-6 172 

30-6 378 

45-6 487 
59-5 768 

From this table it will be seen that bromine has a high vapour 
pressure at ordinary temperatures. 

On cooling to — 7-3° C. it is converted into a crystalline mass 
of a lead-grey colour and a metallic glint. At 0° C. it forms a red 
crystalline hydrate with water of the formula Br 2 . ioH 2 0 which 
on heating to 15° decomposes into bromine and water. 

It is soluble in water ; the solubility at various temperatures 
is given in the following table (Dancer) : 



TEMPERATURE PARTS OF BROMINE IN 

0 C. IOO PARTS BROMINE WATER 

5 3-6oo 

IO 3-327 

15 3-226 

20 3-208 

25 3-I67 

30 3-126 



A saturated solution of bromine in water has a yellow colour, 
an acid taste and irritates like bromine. In the air, particularly 
on heating, it loses bromine without becoming acid. In sunlight, 
however, hydrobromic acid is formed. 

Bromine is soluble in alcohol, ether, chloroform and carbon 
disulphide, but alcoholic and ethereal solutions rapidly decompose. 
It dissolves more readily in aqueous solutions of hydrobromic 
acid, potassium bromide and hydrochloric acid. Solutions in the 
last may be obtained containing 13% bromine. 

The latent heat of volatilisation of bromine at 58° C. is 45-6 
calories. 

The chemical properties of bromine are similar to those of 
chlorine, but it is less active. Thus, for example, in order to 
bring about the reaction with hydrogen it is not sufficient to 
expose the mixture to light, but it is also necessary to heat it. 

With alkaline reagents it reacts in a similar manner to chlorine. 



40 



THE HALOGENS 



With non-metals of the fourth and fifth groups it reacts so 
vigorously that they inflame. 

Bromine in a dry condition either reacts not at all or only 
partially with the common metals, though it attacks aluminium 
violently. Magnesium is the most resistant metal. Mercury 
reacts directly with bromine to form insoluble mercurous bromide. 
The presence of moisture always increases the corrosive action of 
this substance on metals. 

Commercial bromine usually contains chlorine, iodine and some 
organic bromine compounds. 

It has a vigorous toxic action on the organism and provokes 
irritation of the eyes. The fatal concentration is 220 mgm./cu. m. 
for 30-60 minutes' breathing. 

Analysis of the Halogens 

Detection of Chlorine 

Chlorine may be simply recognised by means of its charac- 
teristic pungent odour. According to experiments carried out 
by Smolczyk, 1 chlorine can be detected by means of its odour 
at a dilution of 5 parts per million of air (= 14 mgm./cu. m. of 
air at 20° C). Confirmation of the presence of chlorine by 
chemical methods may be carried out by one of the following 
reactions : 

Flame Method, Detection of chlorine by this method is based 
on the reaction noticed by Beilstein, 2 according to which chlorine 
burnt at the base of a spiral of copper wire suspended in the 
flame of a spirit lamp produces volatile copper chloride which 
colours the flame a bright green. 

The apparatus usually employed for this test consists of an 
ordinary spirit lamp or gas burner carrying in the flame a small 
copper spiral. The gaseous mixture to be tested is introduced 
into the base and interior of the flame, not merely at the spiral. 
In presence of chlorine a change of colour from bluish-violet to 
bright greenish-yellow is seen. The limit of sensitivity is 1 in 

20.000. 3 

This reaction is given also by bromine and iodine, as well as by 
all substances containing halogen atoms in the molecule. The 
sensitivity in these cases depends only on the quantity of halogen 
present in the substance under test. 

Decolorisation of Indigo Solution. By passing a gaseous 

1 Smolczyk, Die Gas-maske, 1930, 27. 

! Beilstein, Ber., 1872, 5, 620. 

3 Lamb, /. Am. Chem. Soc, 1920, 42, 78. 



CHLORINE : DETECTION 



4i 



mixture containing chlorine through a solution of indigo, the 
blue of the latter is discharged by the oxidation of the indigo to 
isatin. 

Method with Potassium Iodide. Chlorine may also be detected 
by its property of liberating iodine from potassium iodide : 

2KI + Cl 2 = 2KCI + I 2 . 

The iodine which separates may be recognised either by the 
reddish-violet colouration which it imparts to chloroform or to 
carbon disulphide, or by the blue colouration which is produced 
with starch solution. This latter reaction can be adapted in 
practice by employing starch-iodide paper, 1 which when exposed 
even for a short period to an atmosphere containing chlorine 
assumes a blue colour more or less intense according to the 
concentration of chlorine present. According to the experiments 
of Smolczyk 2 a content of 14 mgm. chlorine per cu. m. of air 
produces a change in the colour of starch-iodide paper within 
3-5 seconds. 

Aniline Method. Chlorine brought into contact with a solution 
of aniline hydrochloride produces a wine-red colouration which 
becomes blue. 3 The aniline hydrochloride solution is prepared 
by dissolving 2 ml. aniline in 8 ml. hydrochloric acid and 40 ml. 
water. 

Reactions of Chlorine Water. Chlorine in gas mixtures can also 
be detected by bubbling the gas to be tested through water ; 
chlorine water is formed and the presence of chlorine can be 
confirmed in this : 

(a) With silver nitrate by the formation of a white precipitate 
of silver chloride : 

3 C1 2 + 6AgN0 3 + 3 H 2 0 = 5AgCl + AgC10 3 + 6HN0 3 . 

(b) With metallic mercury by the formation of a grey precipitate 
of mercurous chloride : 

2 Hg + Cl 2 = Hg 2 Cl 2 . 

This last reaction allows chlorine to be recognised in presence of 
hydrochloric acid or phosgene as these substances do not react 
with mercury. 

1 Preparation of the Test Papers. One part of starch is boiled with 100 parts 
of water and the solution filtered. To the nitrate 5 parts of potassium iodide are 
added and the strips of filter paper are immersed in this. They are then allowed 
to dry in the air and kept in a closed vessel. The period during which they may 
be stored depends upon the method by which they have been prepared and the 
care with which they have been stored. When the papers are prepared according 
to the instructions of Storm (/. Ind. Eng. Chem., 1909, 1, 802, or Chem. Zentr., 
1910, 1, 1806) and stored in a glass-stoppered bottle they may be kept for 8 years. 

2 Smolczyk, Die Gas-maske, 1930, 29. 

3 Ganassini, Boll, chim.farm., 1904, 43, 153. 



4 2 



THE HALOGENS 



Detection of Bromine 

Bromine may be detected by the bluish-violet colour which it 
imparts to a paper impregnated with Schiff's reagent. This 
paper may be prepared by soaking a narrow strip of filter paper 
in an aqueous solution containing 0-025% fuchsine decolorised 
with sulphur dioxide, and allowing to dry. 

The presence of bromine vapour may also be recognised by 
bubbling the gaseous mixture to be tested through water and 
testing the solution obtained by one of the following methods : 

(a) Addition of a solution of potassium iodide and recognition 
of the iodine freed by means of starch paste. 

(b) Addition of a solution of phenol, which in the presence of 
bromine produces a white or faintly yellowish flocculent precipitate 
of tribromophenol, C 6 H 2 Br 3 .OH (m.p. 93° to 94° C). If the 
bromine is in excess, however, a whitish-yellow crystalline 
precipitate of tribromophenol bromide (m.p. 132° to 134° C.) is 
formed. 1 

Finally, bromine may be recognised either by the red colouration 
which is produced with fluorescein, due to the formation of 
tetrabromofluorescein or eosin, or by the fluorescence produced 
by passing it through a dilute solution of resorufin in alkali 
carbonate. This reaction of bromine also forms the basis of a 
method of quantitative determination of the element in air. 2 

Quantitative Determination of Chlorine 

The quantitative determination of chlorine may be carried 
out either by a volumetric or a gravimetric method. 

Volumetric Method (Bunsen). This method depends on the 
determination of the quantity of iodine freed by chlorine when 
brought into contact with a solution of potassium iodide. 

In proceeding to analyse a sample of gas, if the concentration 
of chlorine is not too great, it is advisable to draw the gas by 
means of a pump or an aspirator through an aqueous solution of 
potassium iodide 3 contained in an ordinary bubble absorber 
large enough to ensure the complete reaction of the chlorine with 
the potassium iodide. If, however, the gas contains a large 
proportion of chlorine it is preferable to introduce it into a glass 
globe fitted with a tap and previously evacuated. The volume of 
this should be known. A solution of potassium iodide is then 

1 Kobert, Compendio di tossicologia pratica, Milan, 1915, 146 ; Benedict, 
Ann., 1879, 199, 127. 

2 H. Eichler, Z. anal. Chem., 1934, 99, 272. 

3 In order to prepare this solution, 1 part by weight of potassium iodide (free 
from iodine) is dissolved in 10 parts of water. The solution should be colourless 
and remain so when a few drops of dilute sulphuric or hydrochloric acid are 
added. 



CHLORINE AND BROMINE: DETERMINATION 43 



introduced into the globe, which is allowed to stand. By this 
method one equivalent of chlorine sets free one equivalent of 
iodine, which remains dissolved in the excess potassium iodide. 
Then the amount of iodine in this solution is determined by the 
usual method of analysis with sodium thiosulphate. 

1 ml. o-i N Na 2 S 2 0 3 = 0-00354 gm. CI 

= 1-1228 ml. gaseous chlorine 

at 20° and 760 mm. 

Gravimetric Method. 1 This method is based on the determina- 
tion of the quantity of sulphuric acid formed by the action of 
chlorine on sodium thiosulphate. 

In carrying out this analysis a measured quantity of the liquid 
in which chlorine is to be estimated is taken. It should contain 
no sulphuric acid. A slight excess of sodium thiosulphate is 
added and the whole warmed for a short time in a vessel closed 
with a tightly fitting stopper. The odour of chlorine completely 
disappears. A slight excess of hydrochloric acid is then added 
and the whole heated to boiling to decompose the excess 
thiosulphate. The liquid is then filtered and the sulphuric acid 
precipitated in the filtrate with barium chloride in the usual way. 

For the rapid determination of the percentage of chlorine and 
carbon dioxide in air, the following method is recommended 2 : 

Two 100-ml. burettes are filled with the gas to be examined ; 
in one the chlorine is absorbed with a solution of potassium 
iodide and the iodine liberated is determined by titration with a 
decinormal solution of sodium thiosulphate ; in the second 
burette both the chlorine and the carbon dioxide are absorbed 
by sodium hydroxide solution, and the difference in the diminu- 
tions of volume in the two burettes gives the volume of the 
carbon dioxide. 

For the determination of chlorine in presence of phosgene 
see p. 88. 

Quantitative Determination of Bromine 

To determine bromine quantitatively in air a measured quantity 

of the gas to be examined is passed through 15-20 ml. of a freshly 

prepared potassium iodide solution (10%). By this means one 

equivalent weight of bromine liberates one equivalent weight of 

iodine, which may then be estimated by titration with a standard 

solution of sodium thiosulphate according to the method described 

above for chlorine. 

1 ml. o-i N Na 2 S 2 0 3 = 0-00799 gm- bromine. 

1 Wicke, Ann., 1856, 99, 99. 

» Offerhaus, Z. angew. Chem., 1903, 16, 1033. 



CHAPTER V 



COMPOUNDS OF DIVALENT CARBON 

Carbon, like several other elements, exhibits a variable 
valency in its compounds. Thus it is tetravalent in the greater 
number of organic compounds, trivalent in triphenylmethyl, and 
pentaphenylethyl, etc., and divalent in carbon monoxide, fulminic 
acid and its derivatives, in the halogenated compounds of 
acetylene, etc. 

Substances containing a divalent carbon atom have in general 
the following properties : 

(1) They react with halogens, hydrogen acids of the halogens, 
oxygen, etc., forming addition products. 

(2) They have powerful and disagreeable odours (with the 
exception of carbon monoxide). 

(3) They are toxic. 

Among these substances, carbon monoxide merits special 
attention. According to some authorities it will play a great 
part in future warfare. 

Several possible methods of using it are at present in the 
suggestion stage, but the methods suggested do not seem to have 
found practical application. 1 

The method of applying carbon monoxide which was first 
thought of, was in the form of the metal carbonyls — iron- 
pentacarbonyl and nickel tetracarbonyl — which in the presence 
of catalysts such as the activated carbon used in anti-gas filters 
evolve carbon monoxide. 

These compounds are unstable, however, and easily decompose, 
even by simple exposure to light . For this reason it does not seem 
that in practice it will be possible to obtain a sufficient concentra- 
tion in the anti-gas filter of these substances to develop by 
contact with the activated carbon a dangerous concentration of 
carbon monoxide in the respirator. 

Another possible mode of using carbon monoxide which has 
been suggested is in the form of a solution in a suitable liquid. 
Carbon monoxide dissolves to a considerable extent in liquid 
gases such as ammonia and can be liberated from these solutions 

1 Hanslian, Der chemische Krieg, Berlin, 1937, Part I, 327. 
44 



CARBON MONOXIDE: FORMATION 



by evaporation. Suitable solvents according to Hanne belong 
to the class of amines. 1 

The last suggestion for applying carbon monoxide is in 
admixture with hydrocyanic acid. Such a mixture would be 
capable of passing through the anti-gas niters in actual use. 2 

Among the compounds containing divalent carbon atoms the 
acetylene mono- and di- halides may be mentioned. These have 
a certain interest from the point of view of the chemistry of the 
war gases. The following structural formula is given to these 
compounds 3 : 

C=C( 

X ' 

The halogen derivatives of acetylene differ from the halogen 
derivatives of the paraffin series in being more toxic, and in 
being unstable and spontaneously inflammable. The instability 
and inflammability diminish considerably on passing from the 
chlorine to the bromine derivatives and are less still in the iodine 
derivatives. 4 

So far as the physiopathological properties have been studied 
it has been observed that the iodo- derivatives are more toxic 
than the bromo-compounds and are also more poisonous than 
hydrocyanic acid. The toxic action exhibited by substances of 
this class has been attributed to the presence of the divalent 
carbon atom which, as already mentioned, has a greater chemical 
affinity than tetravalent carbon. 

In spite of the high toxicity, these compounds have not yet 
found application as war gases, above all because of their 
instability and the difficulty of preparing them on the industrial 
scale. 

Compounds containing a divalent carbon atom united to a 
nitrogen atom are described in Chapter XIII. 

1. Carbon Monoxide. CO. (M.Wt. 28) 

Carbon monoxide was not employed during the war of 1914-18 

as a war gas, but its toxic action has been established on several 

occasions in the field. 
Carbon monoxide is formed whenever the combustion of 

carbon is incomplete, and from the military point of view is, in 

particular, developed during the deflagration of explosive 

1 Hanne, Industrie Chimique, 1935, 22, 322. 

a Instructions sur la difense passive, Lavauzelle, Paris, 1934. 

3 J. Lawrie, /. Am. Chem. Soc, 1906, 36, 487 ; Ingold, /. Chem. Soc, 1924, 
1528. 

4 Straus and coll., Ber., 1930, 63. 1872. 



46 COMPOUNDS OF DIVALENT CARBON 



substances both at the time of firing and on explosion of the 
projectile, also in the detonation of mines, etc. 

The amount of carbon monoxide formed during these processes 
varies notably with the explosive substance, the density of the 
charge, the temperature, pressure, etc. The usually accepted 
data for explosives of different types are as follows : 

i kg. black powder yields 279 litres gas at 0° C. 

1 kg. nitroglycerine yields 713 ,, ,, 

1 kg picric acid yields 828 

1 kg. guncotton yields 859 

In normal deflagration the following percentages of carbon 
monoxide are formed : 

Black powder . . . about 10% 

Powder B . 33% 

Dynamite . . . . ,.35% 

Guncotton . . . „ 40% 

Trinitrotoluol . . . ..55% 

Laboratory Preparation 

Carbon monoxide is usually prepared by the dehydration of 
formic acid by means of sulphuric acid 1 : 

HCOOH + H 2 S0 4 = CO + H 2 S0 4 .H 2 0. 

Concentrated sulphuric acid is placed in a flask closed with a 
three-holed stopper. One of the holes carries a tap-funnel, 
another a thermometer and the third a gas delivery tube. The 
flask is heated to 100° C. and then industrial formic acid (about 
98%) is allowed to flow in slowly while the temperature of the 
liquid is maintained at 100° C. From 175 gm. formic acid, 
100 gm. carbon monoxide are obtained. 

Industrial Manufacture 

See the usual treatises on inorganic chemistry and the section 
" Phosgene " in the present volume (p. 62). 

Physical and Chemical Properties 

A colourless, odourless gas. B.p., — 190 0 C. Critical tempera- 
ture, — 135-9° C. Critical pressure, 35-5 atmospheres. Density, 
0-967. 

It is only very slightly soluble in water : at 0° C, 1 litre of 
water dissolves 32 ml. ; at 20 0 C, 23 ml. It dissolves readily in 
alcohol and other organic solvents. 

It is absorbed by aqueous ammonia and also by ammoniacal 
or hydrochloric acid solutions of cuprous salts. 

1 A. Klemenc, Die Behandlung und Reindarstellung von Gasen, Leipzig, 
1938, 122. 



CARBON MONOXIDE ; PROPERTIES 47 



It burns with a violet flame. Mixtures of carbon monoxide 
and air in certain proportions are inflammable. The upper and 
lower explosive limits at room temperature are respectively 
73-4% and 16-2% of CO.* 

The chemical behaviour of carbon monoxide depends on the 
presence of the divalent carbon atom in the molecule : the 
addition of oxygen to form carbon dioxide, the addition of 
chlorine to form phosgene, etc. 

By heating under pressure with sodium hydroxide sodium 
formate is produced : 

CO + NaOH = HCOONa 

Highly reducing metals like aluminium and (powdered) 
magnesium react on heating with carbon monoxide, forming the 
corresponding oxide and freeing carbon. 

Some metals, as nickel, iron and cobalt, form additive 
compounds of the formulae Ni(CO) 4 , Fe(CO) 4 , Fe(CO) 6 , Co(CO) 4 . 

Platinum chloride forms several additive compounds with 
carbon monoxide : PtCl 2 .CO; PtCl 2 .2CO; PtCl 2 .3CO, which 
are all yellow and which decompose easily by the action of water, 
separating platinum in a finely divided state and giving carbon 
dioxide and hydrochloric acid. 

Oxygen, ozone and hydrogen peroxide do not oxidise carbon 
monoxide at ordinary temperatures, but in presence of catalysts, 
as, for instance, " Hopcalite " (a mixture of 60% Mn0 2 and 
40% CuO) , even atmospheric oxygen will convert carbon monoxide 
to carbon dioxide. Because of this behaviour, " Hopcalite " is 
employed in filters for defence against carbon monoxide. 

The conversion of carbon monoxide to carbon dioxide is also 
brought about by the action of other oxidising agents as silver 
oxide, potassium permanganate, iodic acid, chromic acid, 
mercuric chr ornate, etc. 

Carbon monoxide easily reacts with haemoglobin forming 
carboxy-haemoglobin. The affinity of carbon monoxide for 
haemoglobin is some 200 times as great as that of oxygen. 

2. Iron Pentacarbonyl. Fe(CO) 6 (M.Wt. 195-8) 

Iron pentacarbonyl was obtained in 1891 by Ludwig Mond 2 
by the action of carbon monoxide on iron, prepared from ferrous 
oxalate. The yield obtained was about 1% of the theoretical 
from the iron employed. 3 

1 J. Schmidt, Das Kohlenoxyd, Leipzig, 1935, 229. 

! L. Mond and Langer, /. Chem. Soc, 1891, 59, 1090. 

3 Berthelot, Compt. rend., 1891, 112, 1343 ; R. Mond, Chim. et Ind., 1929, 
21, 681. 



48 COMPOUNDS OF DIVALENT CARBON 



The reaction for the formation is as follows : 
Fe + 5CO = Fe(CO) 5 + 54"4 cal. 
and this takes place more easily at low temperatures and high 
pressures. 

Carbon monoxide may be prepared by the action of dehydrating 
agents on formic acid (see p. 46) . The iron may be prepared from 
other compounds besides ferrous oxalate, but it must have as 
large a reactive area as possible and be of high purity. 

Iron pentacarbonyl is formed at a pressure of 100-200 atmo- 
spheres in a tube heated externally to a temperature of 150° to 
200° C. 

The iron pentacarbonyl formed is drawn as vapour with the 
current of carbon monoxide out of the reaction tube into a 
refrigerant where it condenses. The excess carbon monoxide is 
collected in a gas holder and may be returned in cycle. 1 

The industrial preparation of iron pentacarbonyl has presented 
much difficulty from the beginning. The difficulties have been 
due to 2 : 

(1) The presence of oxygen even in minute quantity, either in 
the iron or in the carbon monoxide. 

(2) The precipitation of the pentacarbonyl on the iron during 
the reaction. 

(3) The presence of impurities in the iron. 

Physical and Chemical Properties 

Iron pentacarbonyl is a liquid boiling at 1027° C. at 767 mm. 
of mercury and having a melting point of — 20° C. (Dewar). 
Density, 1-4665 at 18 0 C. Coefficient of thermal expansion 
between o° and 21° C, 0-00121 ; between 20 0 and 40 0 C, 0-00128, 
and between 40° and 60° C, 0-00142. Latent heat of evaporation, 
39*45 gm- cals. 

In the following table, the vapour tension and the volatility 
at various temperatures are given 3 : 



TEMPERATURE 


VAPOUR TENSION 


VOLATILITY 


°C. 


MM. MERCURY 


MGM. /LITRE 


-7 


14 


l60 


0 


16 


l80 


18-4 


28 


3IO 


35 -o 


52 


58O 


57-o 


135 




78-0 


311 





1 D.R.P., 428,042 ; 436,369 ; 440,770, etc. 

2 A. Mittasch, Z. angew. Chem., 1928, 41, 827. 

3 J. Dewar and H. Jones, Proc. Roy. Soc. (Lond.), 1905, 76, 558. 



IRON PENTACARBONYL : PROPERTIES 49 



It is insoluble in water which slowly decomposes it in the cold. 
It is soluble in most organic solvents (acetone, benzene, etc.). 
The solutions are generally brown in colour and slowly decompose 
in the air forming a precipitate of iron hydroxide. 

Iron pentacarbonyl when exposed to the action of light 
decomposes to form carbon monoxide and a solid crystalline 
substance of a golden-yellow colour and the formula Fe 2 (CO) 9 , 
diferro-nonacarbonyl 1 : 

2 Fe(CO) 5 = Fe 2 (CO)„ + CO 

This decomposition does not take place if a solution of iron 
pentacarbonyl in nickel carbonyl is exposed to light, perhaps 
because of the formation of a stable compound of the formula 
NiFe(CO) 9 (Dewar). 

When mixed with air, iron pentacarbonyl decomposes on 
exposure to sunlight in a very few minutes with formation of 
carbon monoxide and iron oxide. 

It is very sensitive to the action of heat ; on warming to about 
200° C. under ordinary pressure it decomposes completely to 
iron and carbon monoxide. 2 This decomposition, however, takes 
place at a much lower temperature in the presence of substances 
having a porous structure. Thus in the presence of iron, about 
6o° C. is sufficient and in the presence of activated carbon, 
magnesium oxide, etc., it takes place even at ordinary 
temperatures. 3 

The vapour of iron pentacarbonyl burns in the air with a 
brilliant flame and a characteristic spectrum (Mittasch). By 
directing this flame against a porcelain capsule, a black deposit 
of partly oxidised iron forms. 

Alcoholic solutions of sodium or potassium hydroxide easily 
absorb iron pentacarbonyl 4 ; the resulting solution has vigorous 
reducing properties. 

Concentrated nitric and sulphuric acids react with iron 
pentacarbonyl according to the equation : 

Fe(CO) 5 + H 2 S0 4 = FeS0 4 + H 2 + 5CO. 

On shaking iron pentacarbonyl with a dilute solution of 
hydrogen peroxide, colloidal ferrous hydroxide separates. 

With chlorine it reacts easily, forming ferric chloride and 
carbon dioxide. With bromine it reacts similarly ; with iodine 
the reaction is much slower (Dewar). 

1 Speyer, Ber., 1927, 60, 1424. 

2 Dewar and Jones, Proc. Roy. Soc. (Lond.), 1907, 79, 66. 

3 Hloch, Gasschutz und Lufischutz, 1933. 180. 

« Freundlich, Ber., 1923, 56, 2264 ; Z. anorg. Chem., 1924, 141, 317. 



50 COMPOUNDS OF DIVALENT CARBON 



According to recent researches, by allowing bromine to drop 
into a solution of iron pentacarbonyl in pentane, a yellow 
precipitate of Fe(CO) 4 .Br 2 is formed. 1 

Iron pentacarbonyl reacts with mercuric chloride with separa- 
tion of a white substance according to the equation 2 : 

Fe(CO) 8 + 2 HgCl 2 + H 2 0 = Fe(CO) 4 .Hg 2 Cl 2 + C0 2 + 2HCI. 

It possesses reducing properties, especially in alkaline solution. 

fee nitrobenzene is reduced to aniline, ketones to alcohols, 3 etc. 

If also has a dehalogenating action, reacting with carbon 
tetrachloride to form carbon monoxide, phosgene and hexachloro- 
ethane, while the iron is converted to ferric chloride (Mittasch). 

It does not react with ammonia, but the basic amines, like 
pyridine, react to produce carbon monoxide. With hydrazine 
it reacts vigorously, forming a syrupy substance with an intense 
red colour ; for each molecule of hydrazine, four molecules of 
carbon monoxide are set free. 4 

The vapour of iron pentacarbonyl is absorbed by activated 
carbon, which catalytically decomposes it with formation of 
carbon monoxide. 

Alumina also absorbs iron pentacarbonyl vapour to the extent 
of about 2-5% by weight. If the alumina containing the absorbed 
pentacarbonyl is exposed to sunlight, it becomes red in colour 
and the theoretical quantity of carbon monoxide in the absorbed 
iron pentacarbonyl is evolved (Dewar). 

According to Mittasch, the toxicity of iron pentacarbonyl is 
relatively slight. It is necessary, however, to take into account 
the carbon monoxide formed by its decomposition. 

3. Dibromoacetylene. CBr 2 = C. (M.Wt. 183 8) 

Dibromoacetylene was prepared in 1903 by Lemoult 5 by the 
action of alcoholic potash on tribromoethylene : 



Later, Lawrie 6 also obtained it by the same method, but did 
not establish the structure with the divalent carbon atom. 
Recently, this compound has been prepared by Nekrassov 7 by 



1 W. Hieber and G. Bader, Ber., 1928, 61, 1717. 

2 Hock, Ber., 1928, 61, 2097. 
8 D.R.P., 441,179/1925. 

4 W. Hieber and coll., Ber., 1928, 61, 558. 
6 Lemoult, Compt. rend., 1903, 136, 1333. 
• Lawrie, /. Am. Chem. Soc, 1906, 36, 490. 
' Nekrassov, Ber., 1927, 60, 1757. 



CBr. 



2 




CHBr 



+ HBr 



DIBROMOA CETYLENE 



5i 



the action of an ethereal solution of cyanogen bromide on 
magnesium dibromoacetylene : 

CMgBr ,Br 

"I +2 CNBr = C=C< + 2 MgCNBr 

CMgBr N Br 



Laboratory Preparation 

26-5 gm. tribromoethylene and 10-5 gm. 82% potass^PF 

hydroxide are placed in a separatory funnel of about 1 litre 
capacity. The stopper of the funnel has two holes, through one 
of which passes a small tap-funnel and through the other a simple 
tap. The contents are treated in an atmosphere of nitrogen with 
35-50 gm. alcohol (95%), cooling meanwhile in a stream of water. 
After 2 hours, 400-500 ml. air-free water are added. At the 
bottom of the separatory funnel an oily layer of dibromoacetylene 
collects ; this is run off into a flask filled with carbon dioxide and 
distilled in an atmosphere of carbon dioxide by heating in an oil 
bath to ioo° to 120° C. (Lawrie). 



Physical and Chemical Properties 

Dibromoacetylene is a colourless heavy liquid which boils at 
76° to 76-5° C., 1 has an unpleasant odour and a density of about 2. 
It is soluble in most organic solvents. 

It is a very unstable substance. It inflames in the air, burning 
with a red flame. On heating it decomposes with explosive force 
and deposits carbon. In absence of oxygen it is not a dangerous 
substance. 

With damp oxygen it reacts to form hydrobromic acid, oxalic 
acid and a bromine-compound which has strongly irritating 
properties (Lemoult). 

It reacts with bromine to form tetrabromoethylene, colourless 
crystals melting at 55° to 56° C. It reacts with iodine to form 
diiodo-dibromoethylene, crystals with m.p. 95° to 96° C. 

At ordinary temperatures, hydriodic acid adds on to the 
molecule forming dibromoiodoethylene, Br 2 C = CHI, a liquid 
boiling at 91 0 C. at 15 mm. pressure. Density, 2-952 at 24° C. 
(Lawrie). 

Dibromoacetylene is a substance of highly toxic properties. 
Inspiration of its vapour causes violent and prolonged headaches 
and general debility (Lawrie) . 



1 Lbmoult, Compt. rend., 1903, 137, 55. 



52 COMPOUNDS OF DIVALENT CARBON 



4. Diiodoacetylene. CI 2 = C. (M.Wt. 277 8) 

Diiodoacetylene was obtained in 1865 by Berend, 1 together 
with other substances, by the action of an ethereal solution of 
iodine on silver acetylide. But it was only in 1885 that Bayer 2 
recognised it as an individual substance. He prepared it together 
with tetraiodoethylene by the action of iodine on calcium 
carbide 3 : 

CaC 2 + 2l 2 — > CI 2 = C + Cal 2 . 

According to Biltz 4 a more practicable method is by the action 
of acetylene on an alkaline solution of iodine in potassium iodide : 

C2H 2 + KIO + I 2 -^ CI 2 = C + KI + H 2 0. 

Recently 5 a new method has been elaborated, which consists 
in bubbling acetylene through a solution of iodine in liquid 
ammonia. The yield in this reaction is 90-97%. 

Laboratory Preparation 

300 ml. of a seminormal solution of potassium hydroxide are 
introduced into a flask furnished with a tap-funnel, an electric 
agitator and a tube for the introduction of gas. A rapid current 
of acetylene, previously washed with a solution of basic lead 
acetate, is passed in, meanwhile stirring and cooling strongly and 
dropping in from the tap-funnel a solution of 32 gm. iodine and 
35 gm. potassium iodide in 25 ml. water until the colour of the 
iodine persists in the reaction mixture. This operation lasts 
30-40 minutes. 

The precipitate obtained is filtered off, washed with water, 
dried in a desiccator, and, if necessary, crystallised from ligroin. 
Yield almost theoretical (Biltz). 

Physical and Chemical Properties 

Diiodoacetylene forms white crystals melting at 78-5° C. which 
have a strong, disagreeable odour very similar to that of phenyl 
isocyanide. It has a high volatility and is insoluble in water, but 
soluble in alcohol, ether, etc. Exposed to light it slowly becomes 
red with separation of iodine. 

When heated in either a closed or an open tube, diiodoacetylene 
decomposes explosively, forming carbon and iodine. The 
temperature of decomposition is about 125° C. (Vaughn). It also 
explodes on rubbing in a mortar. 

1 Berend, Ann., 1865, 135, 257. 

1 Bayer, Ber., 1885, 18, 2275. 

3 Biesalsky, Z. angew. Chem., 1928, 41, 720. 

* Biltz, Ber., 1904, 37, 4415. 

6 Vaughn and Nieuwland, /. Am. Chem. Soc, 1932, 54, 788. 



DIIODOA CETYLENE : CHEMICAL PROPERTIES 53 



It oxidises slowly in air, especially in neutral solution, forming 
carbon monoxide and tetraiodoethylene : 

2C = Cljj + 0 2 = 2CO + CI 2 = CI 2 . 

This oxidation also takes place if sodium hydroxide is added 
to an alcoholic solution of diodoacetylene. 1 

By passing a current of dry chlorine into diiodoacetylene or 
into its solution in chloroform, white needles of hexachloroe thane 
(m.p. 186-5° C.) are obtained after removing the excess chlorine. 

By the prolonged action of bromine on diiodoacetylene 
hexabromoethane is similarly obtained in the form of white 
crystals, which melt at 210° to 215° C. with separation of bromine. 
Under suitable conditions several compounds of bromine and 
iodine may be obtained, as dibromodiiodoethylene, triiodobromo- 
ethylene, etc. (Berend and Nef). 

Concentrated nitric acid or chromic acid in acetic acid solution 
reacts to form carbon dioxide and iodoethylene. 

With fuming nitric acid a very violent reaction takes place 
with evolution of carbon dioxide and separation of iodine and of 
triiodovinyl nitrate, which has the formula 

CI 2 

II 

CION0 2 

and forms yellow crystals (Nef) . 

It has powerfully toxic properties, the vapour strongly 
irritating the mucous membranes and particularly the eyes (Nef). 
Iodine separates as it acts on the organism, though it partly 
penetrates the tissues without decomposition. 2 

Analysis of Divalent Carbon Compounds 

Detection of Carbon Monoxide 

The various reactions that have been proposed for the detection 
of carbon monoxide depend on its reducing properties and its 
power of reaction with haemoglobin. 

The following are the principal : 

(1) Silver Nitrate. (A solution of silver nitrate to which 
sufficient ammonia has been added to redissolve the precipitate 
which first forms.) By shaking the gas containing carbon 
monoxide with this solution, a black precipitate is produced. 3 
Sensitivity : 0-04%. 

1 Nef, Ann., 1898, 298, 341. 

2 Biltz, Ber., 1897, 30, 1201. 

s Kast and Seixe, Gas- und Wasserfach., 1927, 69, 812. 



54 COMPOUNDS OF DIVALENT CARBON 



(2) Palladium Chloride. This employs 0-2% aqueous solution 
of palladium chloride, or palladium chloride paper. 1 The latter 
is prepared just before use by immersing a strip of filter paper 
in a freshly prepared mixture of equal volumes of a 0-5% solution 
of palladium chloride and a 5% solution of sodium acetate. 2 

Sensitivity 3 : 0-05% CO, in a few minutes. 

0-02% CO, in 2-4 hours. 
0*005% CO, in 24 hours. 

These two reactions, with silver nitrate and palladium chloride, 
can only be used to detect carbon monoxide in air which does 
not contain hydrogen sulphide, ammonia or unsaturated 
hydrocarbons. 

Spectroscopic Method. This is the most certain and specific 
method of detecting carbon monoxide. The gas to be tested is 
passed into a dilute solution (1 in 10, or 1 in 100) of blood which is 
then examined spectroscopically. Pure blood gives the spectrum 
of haemoglobin with its two absorption bands of which one is 
narrow and yellow, near the D line, while the other is less intense 
but wider in the green, near to the E line. Carboxyhaemoglobin 
also gives two bands in D and E but of equal width and intensity, 
somewhat closer together and also displaced towards the violet. 

This test is simplified by adding ammonium sulphide to the 
solution to be tested, when the spectrum of oxyhemoglobin is 
substituted for that of haemoglobin, and the two bands in D 
and E disappear and give place to a single band, less intense and 
narrower. The spectrum of carboxyhaemoglobin remains 
unaltered. Sensitivity : 0-05%. 

Detection of Iron Pentacarbonyl 

(1) Method of Pyrogenic Decomposition. The gas to be 
examined is passed through a glass tube, similar to that usually 
employed in carrying out the Marsh test, and heated by means 
of a gas flame. In the presence of iron pentacarbonyl a ring of 
iron oxide is deposited on the cold part of the tube. Carbon 
monoxide may be detected in the gas issuing from the tube by 
one of the methods given above. 

(2) Griffith's Method* The gas to be tested is bubbled through 
a wash bottle containing concentrated sulphuric acid. By 

1 Winkler, Lehrbuch d. Techn. Gasanal., Leipzig, 1927 ; Brunck, Z. angew. 
Chem., 1912, 25, 2479. 

2 Ljungreen, Eng. Pat., 341269/1930. 
8 V. Italien, Toxicologie, 1928, 183. 

* Griffith, /. Soc. Chem. Ind., 1928, 47, 311. 



CARBON MONOXIDE : DETERMINATION 



evaporating to dryness and taking up the residue with water, 
iron may be detected by the well-known Prussian blue reaction. 

Quantitative Determination of Carbon Monoxide 

Of the various methods suggested, the two described here 
enable very small quantities of carbon monoxide to be determined 
in air. Other methods (gas-volumetric, gravimetric, by combus- 
tion, etc.) may be found in the usual books on chemical analysis. 

(i) Iodine Pentoxide Method. This method is based on the 
determination of the iodine liberated in the reaction between 
carbon monoxide and iodic anhydride according to the equation 1 : 

I 2 0 6 + 5CO = 5C0 2 + I 2 . 

Three U-tubes are connected in series, the first filled with 
granular potassium hydroxide, the second with pumice impreg- 
nated with sulphuric acid, and the third with pure anhydrous 
iodic acid which should not liberate iodine when pure air is passed 
through. 2 This last U-tube is connected by glass-to-glass connec- 
tions with a boiling-tube containing sufficient concentrated 
potassium iodide solution to ensure complete absorption of the 
iodine. 

The iodic acid is heated in an oil-bath to about 150 0 C, and a 
measured volume of the gas mixture to be examined is passed 
through at a velocity of about 10 ml. per minute. The iodine 
liberated by the carbon monoxide is carried over by the gas 
stream and bubbles into the potassium iodide solution. After 
the measured volume of gas has been passed, pure air is drawn 
through for some minutes to ensure complete absorption of the 
iodine which remains in the connecting tubes. 

The liberated iodine is titrated with sodium thiosulphate by 
the usual method of analysis. 

According to Froboese, 3 it is preferable to determine, either 
gravimetrically or volumetrically, the carbon dioxide formed in 
the above reaction rather than to titrate the iodine. 

An apparatus utilising the reaction between carbon monoxide 
and iodic acid has been produced by the Mines Safety Appliances. 4 
This permits the determination of the amount of carbon monoxide 
in air in a few seconds with sufficient accuracy for practical 
purposes. A measured volume of gas is passed first through a 

1 M. Nicloux, Compt. rend., 1898, 126, 746; Gautier, Compt. rend., 1898, 
126, 793- 

a It is best not to use the iodic acid of commerce, but to prepare it by the 
action of nitric acid on iodine, as described by Nicloux, Compt. rend., 1912, 1166. 
3 Froboese, Z. anal. Chem., 1915, 54, 1. 

* " Safety in Mines Apparatus," Jour. Set. Instrum., 1932, 9, 327. 



56 COMPOUNDS OF DIVALENT CARBON 



layer of activated carbon and then through a tube containing 
pumice saturated with iodic anhydride and oleum, known as 
" Hoolamite." 1 In the presence of carbon monoxide the tube 
assumes a colour varying from greyish-blue to greenish-blue 
according to the amount of carbon monoxide. By comparison 
with a standard reference-tube the quantity present in the air 
under examination can be determined. 

(2) " Hopcalite " Method. This is based on the catalytic 
oxidation of carbon monoxide when passed through the oxidising 
mixture of manganese dioxide and copper oxide known as 
" Hopcalite." 2 Determination of the percentage of carbon 
monoxide present is carried out by measuring either the quantity 
of carbon dioxide formed 3 or the heat of oxidation. 

The " Draeger-CO-Messer" apparatus measures the rise in 
temperature of the oxidising mixture mentioned above. This 
rise in temperature may be measured either by means of an 
ordinary thermometer or registered on a thermograph. From the 
increase in temperature the percentage of carbon monoxide may 
be obtained from suitable tables. 4 

Quantitative Determination of Iron Pentacarbonyl 

The method of Griffith, already described, may be applied 
to the determination of iron pentacarbonyl by colorimetric 
determination of the Prussian blue formed. 

If the sample has been dissolved in benzine, methyl alcohol, 
etc., it is treated with perhydrol and the iron precipitated with 
ammonia and determined in the usual way as oxide. 5 

1 Hoover, /. Ind. Eng. Chem., 1921, 13, 770; Katz, /. Ind. Eng. Chem., 
1925, 17, 555- 

2 Lamb and coll., /. Am. Chem. Soc, 1922, 44, 738. For the composition of 
Hopcalite, see p. 47. 

3 Grice, Eng. Pat., 343724/1930. 

* Stampe, Von der Kohlen und Mineraldlen, 1931, 3, 227. 
6 Mittasch, Z. angew. Chem., 1928, 41, 827. 



CHAPTER VI 



ACYL HALOGEN COMPOUNDS 

The substitution of carboxylic-hydroxyl in the molecules of 
organic acids by halogen atoms or by the CN group, generally 
confers toxic properties. 

Among the halogen derivatives of acid radicles especial interest 
attaches to phosgene or carbonyl chloride because of its great 
toxic properties, and it was used in the war of 1914-18. 

From its structure it will be seen that phosgene may be 
considered as carbonic acid in which both the hydroxyl groups 
are substituted by chlorine atoms. 

/OH /OH /CI 

co( CO< CO< 

N OH \\ N C1 

carbonic chlorocarbonic carbonyl 

acid acid chloride 

Analogues of phosgene, such as carbonyl bromide have been 
studied at various times, 1 but experiments on the chemical and 
particularly toxicological properties have only been carried out 
in the last few years. 2 

Carbonyl bromide, because of its boiling point (64° C.) and its 
comparative stability to the action of water would be preferred 
as a war gas to phosgene were it not for its lower stability to light 
and its lesser toxicity. 

Recently carbonyl fluoride has also been prepared and studied. 
It is a colourless gas obtained by the action of silver fluoride on 
carbon monoxide. 3 Because of its great sensitivity to water and 
its low boiling point (— 83 0 C.) it appears improbable that it 
would give satisfactory service as a war gas. 

By the substitution of the halogen atoms in the phosgene 
molecule by CN groups it is possible to obtain the following two 
compounds : 

co( co( 

N CN Vn 

cyanoformic chloride carbonyl cyanide 

1 Emmerling, Ber., 1880, 13, 874 ; Bartal, Z. anorg. Chem., 1907, 56, 49. 

2 H. Schumacher and S. Lenher, Ber., 1928, 61, 1671. 

3 O. Ruff, Z. anorg. Chem., 1934. 221, 154. 

57 



58 ACYL HALOGEN COMPOUNDS 



The chloride of cyanoformic acid is obtained by the action of 
the amide of ethyl oxalate on phthalyl chloride. 1 It is an oily 
substance with b.p. 126° to 128° C. at 750 mm. of mercury. 

Carbonyl cyanide has been obtained 2 from diisonitrosoacetone. 
It is a colourless liquid with a boiling point of 65-5° C. at 740 mm. 
Density, 1-124 at 2 °° C. By hydrolysis it decomposes forming 
carbon dioxide and hydrocyanic acid. 

In recent years compounds of the same general type, but 
having the carbonyl group C : O substituted by the oximic 
group C : NOH, have attracted attention as possible war gases. 

(1) Chloroformoxime 3 

CK 

>C = NOH 
H' 

and (2) Dichloroformoxime, the oxime of carbonyl chloride, 4 

CK 

>C = NOH 
CI' 

The vapours of these substances even in low concentration are 
strongly lachrymatory and produce very painful lesions of the 
eyes which may result in blindness. Both in the solid state and 
in solution they also cause irritation and blistering of the skin. 
This vesicant action results from actual contact of the substances 
with the skin and the blisters heal only very slowly. According 
to Hackmann, 5 very few substances known in the whole of organic 
chemistry are capable of exerting on the human organism 
physiopathological action that is as violent as that produced by 
these oximes. However, their physical and chemical properties 
render them of little use as war gases. 

Recently other compounds analogous with dichloroformoxime 
have been prepared. 6 

(1) Dibromoformoxime, crystals with a melting point of 
68° to 69° C. (Birckenback) or 70 0 to 71 0 C. 7 Distils between 
75° and 85° C. at a pressure of 3 mm. 

(2) Diiodoformoxime , crystals with m.p. 69° C. 

These two substances have a less powerful toxic action than 

1 E. Ott, Chem. Ztg., 1926, 50, 448. 

2 Malachovsky and coll, Ber., 1937, 70 > I012 - 
8 Nef, Ann., 1894, 280, 307. 

* Prandtl, Ber., 1929, 62, 1766; M. Slunesko, Vojenske Technicke Zpravy, 
1927, 14, 155. 

5 Hackmann, Chem. Weekblad., 1934, 31, 366. 

» Birckenbach and Sennewald, Ann., 1931, 489, 9. 

7 J. De Paolini, Gazz. chim. ital., 1930, 60, 703. 



PHOSGENE 



59 



the analogous chlorinated derivatives and especially as vesicants, 
provoke irritation of minor intensity. 

Finally, among the various acyl halogen compounds, formyl 
fluoride, oxalyl chloride, oxalyl bromide, etc., are interesting 
possibilities as war gases. 

Formyl fluoride, H.COF, has been prepared only recently by 
Nesmejanov 1 by the action of benzoyl chloride on a solution of 
potassium fluoride in formic acid. It is a mobile, colourless liquid, 
b.p. — 26 0 C. It dissolves in water, slowly hydrolysing. At 
room temperature either in the liquid or gaseous state, it decom- 
poses in a few hours with the formation of carbon monoxide and 
hydrofluoric acid. 

HCOF — > HF + CO. 

Considered from the physiopathological point of view, formyl 
fluoride is about three times as toxic as acetyl fluoride or 
chloropicrin. 

Oxalyl chloride, (COCl) 2 , has been obtained by the action of 
phosphorus pentachloride on oxalic acid. 2 On heating, it 
decomposes, forming carbon monoxide and phosgene according 
to the equation : 

(COC1), CO + COCljj. 

Oxalyl bromide, (COBr) 2 , has been obtained by the action of 
hydrobromic acid on oxalyl chloride. 3 Heat decomposes it with 
production of carbon monoxide and carbonyl bromide. It reacts 
easily with water forming carbon monoxide, carbon dioxide and 
hydrobromic acid. 

The vapours of these two substances violently attack the 
respiratory organs. 

It has been demonstrated that the stability of the oxalic acid 
halides diminishes in passing from the chlorides to the iodides. 

(COC1), (COBr) 2 (COI), 
Temperature of decomposition . 350 0 150 0 — 80° 

This is analogous to the behaviour of the carbonic acid halides : 

COCl 2 COBr 2 COI 2 
Temperature of decomposition . 400° 100° — 80° 

1. Phosgene. COCl 2 . (M.Wt. 98-9) 

Phosgene, or carbonyl chloride, was obtained in 1812 by Davy 4 

1 A Nesmejanov and E. Kahn, Ber., 1934, 67, 370. 
1 Staudinger, Ber., 1908, 41, 3558. 
3 Staudinger, Ber., 1912, 45, 1595. and 1913, 46, 1431. 
« Davy, Phil. Trans. Roy. Soc, 1812, 102, 144. 



6o 



ACYL HALOGEN COMPOUNDS 



by exposing a mixture of chlorine and carbon monoxide to the 
action of sunlight. 

CO + Clg = COCl 2 . 

This reaction can also be brought about without the influence 
of solar radiation by means of catalysts such as platinum sponge, 
vegetable carbon, animal charcoal, 1 etc. 

Phosgene was employed for the first time as a war gas in 
December, 1915. It was used throughout the war alone or mixed 
with chlorine by emission from containers, while shells were also 
used which contained the same mixture or one including metallic 
chlorides as stannic chloride or other war gases such as chloro- 
picrin, diphosgene, diphenylchloroarsine, etc. 2 

Laboratory Preparation 

In the laboratory, phosgene may be easily prepared by treating 
chloroform with chromic acid mixture 3 : 

2CHCI3 + 30 = 2C0C1 2 + H 2 0 + Cl 2 , 

but by this method the product is impure with chlorine and 
chloroform (5% about). 
Either Erdmann's method, based on the reaction between 




Fig. i. 



1 Paterno, Gazz. chim. itcti., 1878, 8, 233, and 1920, 50, 30. 
s Mameli, Chimica tossicologica, Turin, 1927, 527. 
3 Emmerling, Ber., 1869, 2, 547. 



PHOSGENE : LABORATORY PREPARATION 61 



fuming sulphuric acid and carbon tetrachloride, or the synthetic 
method from carbon monoxide and chloride in presence of 
activated carbon is generally used. 

Preparation from Oleum and Carbon Tetrachloride. 1 100 ml. 
carbon tetrachloride are placed in a flask, A (Fig. i), fitted with 
a stopper through one of whose three holes passes a tap-funnel, B, 
containing 120 ml. oleum (80% free S0 3 ), while a thermometer 
and a reflux condenser pass through the other two holes. The 
flask A is gently heated, while fuming sulphuric acid is allowed 
to enter drop by drop from the tap-funnel, and when this comes 
into contact with the carbon tetrachloride it reacts according to 
the equation : 

S0 3 + CCl, = COCl 2 + SOgClg. 

The phosgene formed is first passed through the wash bottle C, 
containing concentrated sulphuric acid which absorbs sulphur 
trioxide and sulphuryl chloride vapours, and then through two 
condensation receivers, D and E, externally cooled with a 
freezing mixture of ice and calcium chloride. 

After all the oleum has been added, the flask is heated strongly 
for about 5 minutes in order to eliminate all the phosgene. 

In this way phosgene impure with carbon tetrachloride and 
sulphuryl chloride is obtained. According to Popescu 2 it can 
be purified by first heating it to its boiling point (+ 8° C.) and 
then condensing the vapour again after passing it through 
strongly cooled concentrated sulphuric acid. 

Preparation by Synthesis from Chlorine and Carbon Monoxide. 
A wide-mouthed vessel [A, see Fig. 2) is closed with a stopper 




Fig. 2. 



pierced with three holes. Through two of these holes glass 
tubes (B and C) pass to the bottom of the vessel, while through 
the third a very short tube passes and connects with a condenser 

1 H. Erdmann, Ber., 1893, 26, 1993. This method was used in the " Serviciul 
de oparare contra gazelor " of Rumania. Antigaz, 1927, 7, 9. 
8 Popescu, Antigaz, 1927, 7, 11. 



62 



ACYL HALOGEN COMPOUNDS 



(D) filled with granules of activated carbon. The other end of 
the condenser is connected with two receivers, E, F, externally 
cooled with a freezing mixture of ice and calcium chloride. 

Carbon monoxide from a gas holder is passed through a wash 
bottle L containing sulphuric acid, and then by means of tube B 
into the vessel A where it mixes with chlorine introduced through 
the other tube C. The chlorine is passed in at the rate of five or 
six bubbles a second and the carbon monoxide at eight or nine 
bubbles a second. As the two gases pass through the charcoal, 
the latter becomes heated, and water is therefore circulated 
through the outer tube of the condenser to cool it. The phosgene 
as it forms gradually condenses in the two externally cooled 
receivers. 1 

Industrial Preparation 

In Italy and France phosgene was prepared during the first 
years of the war of 1914-18 from carbon tetrachloride and 
fuming sulphuric acid according to the method of Schiittzenberger 2 
modified by Grignard. 3 

This method, though giving a high yield of phosgene (about 
90% of theoretical), consumes much chlorine. For this reason, 
the method was later abandoned in favour of the synthesis from 
carbon monoxide and chlorine which had been used in Germany 
from the beginning. Until a few years ago the synthesis from 
carbon monoxide and chlorine was carried out in presence of 
animal charcoal exclusively, this being conveniently prepared 
from bones and washed first with hot hydrochloric acid, then with 
water, and finally dried. Later it was discovered that vegetable 
carbon prepared from birch wood, lime wood, coconut, etc., had 
greater catalytic activity. 

The synthetic method is nowadays the most widely used for 
the industrial manufacture of phosgene. 

The preparation of the chlorine for use in this process involves 
no points calling for special mention, except that the chlorine 
should be as dry as possible in order to prevent the formation of 
hydrochloric acid during the synthesis. Special care is necessary, 
however, in preparing the carbon monoxide. The most generally 
used process employs the reduction of carbon dioxide obtained 
by the combustion of coke and is carried out in the following 
manner : 

Coke is burned in a special furnace, and the carbon dioxide 

1 Patkrn6 and Mazzuchelli, Gazz. chim. ital., 1920, 50, 30. 

2 SchDttzenberger, Bull. soc. chim., 1869, 12, 198. 
' Grignard, Compt. rend., 1919, 169, 17. 



PHOSGENE : INDUSTRIAL MANUFACTURE 63 



formed is purified by first washing with water and then passing 
it through a series of tubes containing a solution of potassium 
carbonate. 

The carbon dioxide reacts with this solution to form potassium 
bicarbonate according to the equation : 

K 2 C0 3 + C0 2 + H 2 0 = 2KHCO3. 

The solution thus obtained is pumped into a still and heated in 
absence of air, so as to liberate the carbon dioxide again together 
with water vapour. The latter is removed by cooling and then 
passing through concentrated sulphuric acid. 

Carbon dioxide alone is left and this is reduced to carbon 
monoxide by passage through red-hot coke. In order to prevent 
the coke being cooled by the endothermic nature of the reaction 
to a temperature at which the combination no longer takes place 
or occurs only incompletely and very slowly, the carbon dioxide 
is mixed with a definite quantity of oxygen. 

In this way carbon monoxide is obtained impure with carbon 
dioxide which is removed by absorption in caustic soda : 

C0 2 + aNaOH = Na 2 C0 3 + H 2 0. 

After drying, the carbon monoxide is ready for the synthesis. 
The plant for the manufacture of phosgene by the synthetic 
method is shown diagrammatically in Fig. 3. The carbon 




Fig. 3. 



monoxide and chlorine are passed into a mixer A, suitably 
arranging the proportions to correspond with the synthetic 
process which follows. These mixers are simple lead cylinders 



6 4 



ACYL HALOGEN COMPOUNDS 



containing perforated diaphragms. The gases enter tangentially 
at one end of the mixer by two separate tubes, x, y, then are 
mixed in passing through the holes in the diaphragms and leave 
from the other end of the mixer to pass directly into the catalyst 
chamber, B. This may take various forms, but generally consists 
of lead tubes 5-6 m. in height and 1 m. in diameter filled with 
active carbon. The gases enter at the bottom of the chamber 
at a temperature of about 20° C. As the reaction between chlorine 
and carbon monoxide takes place with development of a consider- 
able quantity of heat, the temperature is moderated by external 
cooling. The optimum temperature for the reaction is about 
125° C. and should not exceed 150° C. 1 

The gas mixture containing the phosgene formed is passed 
next through the cooling coils, D, where the greater part condenses 
and is collected in the receiver F. The uncondensed portion then 
enters at the bottom of the absorption tower G, into the top of 
which a fine spray of tetrachloroethane drops, this liquid being 
a solvent for phosgene. The solution obtained passes into the 
still H, in which the phosgene is recovered by heating and 
condenses in the cooler E and collects in the reservoir F, while 
the tetrachloroethane freed from phosgene passes into K and by 
means of the montejus L is carried again to the top of the 
column G. The phosgene obtained in this manner contains 
about 1-5-2% free chlorine and traces of carbon dioxide. 

American Method. At Edgewood the Americans carried out 
the synthesis of phosgene by a method similar to that described 
above, employing, however, a special carbon known as " Filtchar " 
as catalyst. What is particularly interesting about this method 
is the means by which the synthesis from the carbon monoxide 
and chlorine is carried out. 

The catalyst is placed in special boxes of iron covered with 
graphite sheets to protect the iron from the action of the chlorine 
and the temperature during the synthesis allowed to rise of its 
own accord to at least 250° C. However, as in these conditions 
the combination of the two gases is incomplete, in order to prevent 
chlorine and carbon monoxide from escaping uncombined, the 
gases issuing from the catalyst chambers, containing about 85% 
phosgene, are passed into a second series of reaction chambers. 
These are constructed like the first and also contain " Filtchar." 
They are known as the cold catalysts and are kept at a temperature 
of about 95 0 C. 

The resulting gas mixture containing approximately 93-94% 
of phosgene is dried by means of sulphuric acid and then cooled 
1 Chapman, /. Chem. Soc, 191 1, 99, 1726. 



PHOSGENE : PHYSICAL PROPERTIES 65 



by passing through coils immersed in calcium chloride brine at 
— 20° C. At this temperature the phosgene is liquefied, while 
the remaining gas which still contains gaseous phosgene is 
absorbed in linseed oil in a recovery plant. 

Physical and Chemical Properties 

At ordinary temperatures phosgene is a colourless gas with a 
characteristic odour described as that of mouldy hay. On 
cooling to below 8° C. it becomes a colourless, mobile liquid 
boiling at 8-2° C. It solidifies at — 118° C. 1 to a white crystalline 
mass. The technical product is, however, pale yellow or orange 
owing to the presence of coloured impurities, such as chlorine, 
ferric chloride, etc. 

The critical temperature of phosgene is 1817° C. and the 
critical pressure 55-3 atmospheres. A litre of gaseous phosgene 
at 0° C. and 760 mm. weighs 4-4 gm., i.e., three and a half times 
(3-505 to be exact) that of air (1-293). In the following table the 
values of the specific gravity of liquid phosgene are given at 
various temperatures, as well as the values of the specific volume 
(volume of unit weight of liquid phosgene). 



TEMPERATURE 


SPECIFIC 


SPECIFIC 


°C. 


WEIGHT 


VOLUME 


-40 


1-5011 


0-6662 


— 20 


I-46I5 


0-6842 


— IO 


1-4411 


0-6939 


0 


1-4203 


0-704I 


IO 


1-3987 


0-7I50 


20 


1-3760 


0-7260 


40 


1-3262 


0-754I 


60 


1-2734 


0-7853 



The vapour tension of liquid phosgene at temperatures between 
— 15° C. and + 23 0 C. can be calculated from the formula : 

log ^ = 7-5595 -2-^ 

For temperatures between — 13° C. and + 25° C. the vapour 
tension is as follows : 



TEMPERATURE 


VAPOUR TENSION 


°C. 


MM. MERCURY 


- 13-7 


335 


— 10 


365 


- 5 


452 


0 


555 


8-2 


760 


IO 


839-8 


20 


1. 173-4 


25 


i,379 



1 Erdmann, Ann., 1908, 362, 148. 

WAR GASES. 



66 



ACYL HALOGEN COMPOUNDS 



From these data it will be seen that even at ordinary tempera- 
tures phosgene has a high vapour pressure which makes it of low 
persistence as a war gas, although its vapour density is much 
greater than that of air. 

The evaporation of phosgene is also favoured by its low specific 
heat (0-243 calorie) and its low latent heat of evaporation (about 
60 calories). The coefficient of expansion of phosgene is 0-001225 
at o° C. 

Phosgene dissolves readily in many organic solvents, such as 
benzene, toluene, xylene, 1 etc., as well as in fats and oils. From 
these solutions it can be easily removed by a current of dry air. 
Use is made of this property in marketing phosgene as a 30% 
solution in toluene. 

According to Baskerville and Cohen 2 the solubility of phosgene 
in some organic solvents at a temperature of 20° C. is as follows : 

1 gm. phosgene dissolves in i-o gm. benzene 

1-5 „ toluene 
1-2 „ petrol 
1*7 „ chloroform 
3-6 ,, carbon tetrachloride 
i-6 „ glacial acetic acid 

Phosgene is also easily soluble in a'rsenic trichloride (1 part 
AsCl 3 dissolves 100 parts C0C1 2 ) and in sulphur monochloride. 

In the liquid state phosgene dissolves various substances, as, 
for example, chlorine in the following proportions : at o° C, 
6-63% ; at — 15° C, 20-5%, as well as several of the war gases, 
such as dichloroethyl sulphide, chloropicrin, diphenylchloroarsine, 
etc. 

Phosgene is a stable compound at ordinary temperatures and 
in absence of humidity. At somewhat elevated temperatures, 
however, it dissociates fairly easily into carbon monoxide and 
chlorine : 

C0C1 2 = CO + Cl 2 . 

Bodenstein and others 3 have observed that this dissociation 
has the following values at ordinary pressure : 

At 101 0 C. . . 0-45% At 503 0 C. . 67% 

At2o8°C. . . 0-83% At 553° C. . . . 80% 

At309°C. . . 5-61% At 603° C. . . . 91% 

At4oo°C. . . 21-26% At8oo°C. . . . 100% 

1 W. Kireev and coll. have determined the boiling points at ordinary pressure 
and the composition of the vapour from solutions of phosgene in xylene and in 
ethylene dichloride containing amounts of phosgene varying from zero to 35% 
by weight (/. Prikl. Khim., 1935, 949). 

8 C. Baskerville and P. Cohen, /. Ind. Eng. Chem., 1921, 13, 333. 

8 Bodenstein and Dunant, Z. physik. Chem., 1908, 61, 437 ; Bodenstein 
and Plaut, Z. physik. Chem., 1924, 110, 399. 



PHOSGENE : HYDROLYSIS 



67 



When phosgene is passed through incandescent carbon, it 
decomposes according to the equation 1 : 

2C0C1 2 -> CO, + C0 2 . 

By exposure to the light from a mercury vapour lamp in 
presence of oxygen and chlorine, decomposition takes place, and 
as an intermediate product, a compound of the formula COC1 2 is 
formed. By exposure to ultra-violet light chlorine and carbon 
monoxide are formed. 3 

Phosgene in contact with water is hydrolysed even at the 
ordinary temperature according to the equation : 

COCl 2 + H 2 0 = 2HCI + C0 2 . 

Very divergent values are reported in the literature for the 
velocity of this reaction ; according to some workers the hydro- 
lysis of phosgene is instantaneous ; according to others it has a 
measurable velocity. 4 The reaction is strongly influenced by the 
physical state of the phosgene when it is brought into contact with 
the water and also whether the water is in the vapour state or the 
liquid state. Thus, according to Delepine, 5 the reaction velocity 
is not very rapid if the phosgene comes into contact with the 
water vapour normally present in the atmosphere. Experiments 
carried out on this have demonstrated that 1 ml. of gaseous 
phosgene, placed in a 500-ml. stoppered flask with ordinary air, 
still retains the odour of phosgene after 15 days. The normal 
humidity of the air, therefore, does not completely decompose 
phosgene, though there is present in the air more water than that 
necessary for complete hydrolysis. By addition to the flask of a 
drop of water, which is more than sufficient to saturate the air, 
the odour of phosgene is still perceptible after 4 days, but not 
after 12 days. With 2 drops of water the odour disappears in 
2 days. 

The hydrolysis of phosgene actually in contact with water is, 
however, very rapid. 6 Paternd and Mazzucchelli 7 have found 
that by placing 100 ml. water together with a small glass bulb 
containing about 1 gm. phosgene inside a closed vessel, and after 
cooling to 0° C, breaking the bottle and shaking, decomposition 
of the phosgene is complete in barely 20 seconds. 

1 Melnikov, /. Khim. Promiscl., 1932, 9, 20. 

2 G. Rollefson and C. Montgomery, /. Am. Chem. Soc, 1933. 55, 142. 
8 Cohen and Becker, Bey., 1910, 43, 131. 

* Fries and West, Chemical Warfare, 1921, 131 ■. Meyer, Der Gaskampf und 
die chemischen Kampstoffe, 1925, 318; Handleiding in de Chemische Oorlogsvoe 
Ring, Utgave Mavors, 1927, 63. 

6 Delepine, Bull, soc. chim., 1920, [4], 27, 286. 

• S. Vles, Rec. trav. Chim., 1934, 53, 961. 

7 Patern6 and Mazzucchelli, Gazz. chim. Ital., 1920, 50, 30. 

3-2 



68 



ACYL HALOGEN COMPOUNDS 



Although the hydrolytic reaction is irreversible, the products 
formed in the reaction retard further decomposition of the 
phosgene. 

Thus in the case of gaseous phosgene, the carbon dioxide 
formed, being sparingly soluble, immediately saturates the 
surface layer of the water with which it is in contact and the 
greater part remaining in the gaseous state forms an inert layer 
over the liquid preventing further attack of the phosgene. In 
the case of liquid phosgene, it is the hydrochloric acid which 
slows down further decomposition by saturating the water in 
immediate contact. 

It seems, therefore, that such retarding action depends 
principally on the diffusion in the water of the products of 
hydrolysis, which by not diffusing rapidly form a sort of protective 
layer against further decomposition of the phosgene. As soon 
as the products diffuse away into the water, further hydrolysis 
becomes possible. 

The property of retarding the reaction between phosgene and 
water is not specific for hydrochloric acid, but is common to all 
acids. 

Phosgene, which, as stated on p. 57, may be considered as 
carbonic acid chloride, is very reactive, like all acid chlorides. 
It reacts easily with bases ; for instance, with sodium hydroxide 
it forms sodium chloride and sodium carbonate. 

COCl 2 + 4NaOH = 2NaCl + Na 8 C0 3 + 2H 2 0. 

It reacts with calcium hydroxide similarly. Soda-lime is also 
a good neutralising agent for phosgene and has been employed 
for this purpose in the antigas filters of respirators. 

Phosgene does not react with hydrobromic acid even when 
heated to 200 0 C, but hydriodic acid when passed together with 
phosgene through a glass tube 6 m. long, reacts at ordinary 
temperatures with separation of iodine derived from the 
decomposition of iodophosgene. 1 

In the absence of water, phosgene reacts quantitatively with 
sodium iodide in acetone solution according to the equation 2 : 
COCl 2 + 2NaI = CO + I 2 + 2NaCl. 

This reaction is rapid and makes possible the determination of 
small quantities of phosgene in mixed gases (see p. 86). 

Phosgene reacts similarly in contact with an acetone solution 
of lithium bromide : 

COCl 2 + 2LiBr = CO + 2LiCl + Br 2 

1 Staudinger, Ber., 1913, 46, 1426. 

2 Jahresb. der Chem. Tech. Reichsanstalt, 1927, 6, 57. 



PHOSGENE : CHEMICAL REACTIONS 69 



and, according to Perret, 1 this reaction can be employed for the 
quantitative determination of phosgene by measuring the volume 
of carbon monoxide formed. In this determination, the bromine 
does not interfere as it gradually combines to form bromoacetone 
Chlorobromophosgene is formed by the action of aluminium 
bromide or boron bromide on phosgene at 140° C. : 

/CI 
CO< 
N Br 

This is a liquid with a boiling point of 25° C. and specific gravity 
1-82 at 15 0 C. 2 

Phosgene also reacts with ammonia, aniline, dimethyl aniline, 
etc. With ammonia it forms urea. 3 

/CI HNH, /NH, 
CO< + = CO< +2 HC1 

N C1 HNH 2 NH 2 

With aniline, diphenyl urea is formed 4 : 

/CI 2 HNH-C 6 H 5 /NH-C,H 5 



CO 



< + = CO( +2 CgHgNHs . HC1 



N C1 2 HNH-C 6 H 5 NH-C 6 H, 



5 



The reaction of phosgene with aniline, according to Kling and 
Schmutz 5 takes place more rapidly than that with water, and, 
according to Vies, 6 phosgene in contact with a saturated aqueous 
solution of aniline at 0° C. reacts almost only with the aniline. 
A method of analysis of phosgene (see p. 84) has been based on 
this reaction. 

Phosgene reacts with sodamide even at the ordinary 
temperature, according to the equation. 7 

COCl 2 + 3NaNH 2 = NaCNO + aNaCl + 2NH3. 

At a higher temperature, about 250° C, the reaction follows' a 
different course : 

C0C1 2 + 5NaNH 2 = Na 2 CN 2 + zNaCl + NaOH + 3NH3. 

Phosgene acts on dimethyl aniline at ordinary temperatures 

1 Perret, Bull. soc. chim., 1936, 349. 

2 Bartal, Ann., 1906, 345, 334. 

4 R. Fosse and coll., Compt. rend., 1936, 202, 1544. 

4 Hofmann, Ann., 1849, 70, 139. 

6 Kling and Schmutz, Compt. rend., 1919, 168, 773. 

6 S. Vles, Rec. trav. Chim., 1934, 53, 961. 

7 A. Perret and Perrot, Compt. rend., 1934, 199> 955- 



70 ACYL HALOGEN COMPOUNDS 

to give tetramethyl diamino benzophenone, or Michler's 
ketone 1 : 

/CI C 6 H 8 N(CH 3 ) 2 /C 6 H 4 . N(CH 3 ) 2 

CO< + = CO( + 2 HC1 

X C1 C 6 H 8 N(CH 3 ) 2 N C 6 H 4 . N(CH 3 ) 2 

This is a crystalline substance, melting at 173° C, insoluble in 
water but soluble in the common organic solvents. 

In presence of excess phosgene and heating to 50 0 C, />-dimethyl 
amino benzoyl chloride is formed : 

/CI /C 6 H 4 . N(CH 3 ) 2 

CO( i + C 6 H 5 N(CH 3 ) 2 = CO( ci + HC1 

The reaction of phosgene with dimethylaniline when carried 
out in the presence of aluminium trichloride or zinc chloride 2 
gives Crystal Violet, 

With hexamethylene tetramine, or urotropine, an addition 
compound of the following formula is obtained 3 : 

C0C1 2 .2(CH 2 ) 6 N 4 . 

Phosgene reacts with pyridine forming a yellow crystalline 
substance of the formula 4 C 5 H 5 N(C1) .CO. (C1)NC 5 H 5 , which is 
decomposed by water with formation of carbon dioxide according 
to the equation : 

C 6 H 6 N(C1).C0.(C1)NC 8 H 5 + H 2 0 = 2(C 5 H 6 N.HC1) + C0 2 . 

The course of the reaction of phosgene with alcohols and 
phenols is also interesting. With phenols it can react in two 
ways, according to the proportions of the two substances present. 
With one molecule of phenol and one of phosgene, phenyl 
chloroformate is formed : 

C0( C1 + = CO^ + HC1 

N C1 HO-C 6 H 5 X 0 . C 6 H 5 

and with two molecules of phenol, phenyl carbonate : 

/CI OH-C 6 H 8 /O . C 8 H 8 

CO< + = CO< + 2 HC1 

X C1 OH-C„H 8 N 0 . C,H 5 

Because of this peculiar behaviour, sodium phenate is used as 
neutralising agent for phosgene in filters. Alcohols react with 

1 Michler, Ber., 1876, 9, 400. 

2 Hoffmann, Ber., 1885, 18, 769. 

3 Puschin and Mine, Ann., 1937, 532, 300. 

* D.R.P., 109933/1898; Chem. Zentr., 1900, II, 460. 



PHOSGENE : CHEMICAL REACTIONS 



phosgene in a similar manner to phenols 1 ; for example, with 
one molecule of methyl alcohol, methyl chloroformate is formed 
(see p. 102) : 



The latter is a colourless liquid of agreeable odour, boiling at 
90-6° C. and with a density of 1-065 at 17 0 C. It melts after 
freezing at — 0-5° C. It is stable to water and is miscible with 
acids and alkalies. Though insoluble in water, it is soluble in 
most organic solvents. It is transformed into hexachloromethyl 
carbonate or triphosgene by chlorinating agents (see p. 115). 

Phosgene, when left in contact with acetone for about half an 
hour and then distilled, forms isopropenyl chloroformate according 
to the following equation, in which acetone is represented by its 
enolic formula 2 : 



Isopropenyl chloroformate is a liquid, b.p. 93° C. at 746 mm. 
density 1-103 at 20° C, having an irritating odour and powerful 
lachrymatory properties. 

In presence of aluminium trichloride, phosgene reacts with 
ethylene dissolved in carbon disulphide, forming /8-chloro- 
propionic chloride as well as polymerisation products of ethylene. 3 

By the action of phosgene on ethylene glycol at ordinary 
temperatures, glycol carbonate is formed according to the 
equation : 



Glycol carbonate is a liquid boiling at 238 0 C. at a pressure of 
759 mm. and at 152° C. at 30 mm. It is soluble in hot water 
and volatile in steam, soluble in benzol, but in alcohol only with 

1 Dumas, Ann., 1835, 15, 39 ; Bose, Ann., 1880, 205, 229. 

2 M. Matuszak, /. Am. Chem. Soc, 1934, 56, 2007. 

» A. Klebansky, /. Obscei Khim., Ser. A., 1935, 5, 535. 




and with two molecules, methyl carbonate : 




CH 3 CH 3 



C . OH + COC1, = C . OCOCl + HC1 

II II 
CH 2 CH 2 




72 



ACYL HALOGEN COMPOUNDS 



difficulty, soluble in petroleum ether and also in carbon 
disulphide. 1 

In the presence of substances like pyridine, which are capable 
of absorbing the hydrochloric acid formed in the reaction, 
phosgene reacts with glycerol to form glycerol carbonate. 2 

By bubbling gaseous phosgene through ethylene mono- 
chlorohydrin at o° C, /?-chloroethyl chloroformate is formed 



a colourless, irritating liquid, b.p. 152-5° C. at 752 mm. Its 
density at 20° C. is 1-3825. Insoluble in cold water ; hot water 
and alkaline solutions hydrolyse it. 3 

At ordinary temperatures gaseous phosgene reacts with 
a-monochlorohydrin, forming the corresponding carbonate 4 : 



a colourless, heavy liquid, b.p. 156-157° C. at 10-12 mm. Density 
1-55 at 20° C. Sparingly soluble in water. 

In the dry state phosgene has little or no action on most of 
the metals, 5 but in the presence of moisture it has a powerfully 
corrosive action because of the formation of hydrochloric acid. 
It is interesting to note Germann's 6 findings with regard to its 
action on aluminium. According to this worker, phosgene reacts 
with aluminium because the aluminium trichloride which is 
formed is soluble in phosgene. Germann was also able to 
demonstrate that in the presence of aluminium trichloride those 
metals whose chlorides form soluble double salts with aluminium 
trichloride also react with phosgene. 

At temperatures between 350° and 650° C. phosgene reacts 
with metallic oxides, forming carbon dioxide and the 
corresponding chlorides. 7 

Rubber is rapidly attacked by phosgene. 

Phosgene is stored in cylinders like liquid chlorine. Iron 
containers which have been used for long periods for the storage 

1 Vorlaender, Ann., 1894, 280, 186. 
1 D.R.P., 252758. 

■ Nekrassov and Komissarov, /. prakt. Chem., 1929, 123, 160. 

4 Contardi and Ercoli, Gazz. Chim. Hal., 1934, <>4> 522. 

5 Melnikov, /. Khim. Promiscl., 1932, 9, 20. 
• A. Germann, /. Phys. Chem., 1924, 28, 879. 
7 Chauvenet, Compt. rend., 191 1, 152, 89. 





CH 2 C1 



PHOSGENE : ABSORPTION BY CARBON 



73 



or transport of phosgene often contain a small quantity of a 
yellowish-red, heavy liquid which has been found to be iron 
pentacarbonyl (Patern6). 

Activated carbon has a high sorptive capacity for phosgene. 1 
Its capacity for absorbing such substances from their mixtures 
with air depends on various factors : the quality and the quantity 
of the carbon, the humidity, the concentration of the gas mixture, 
the velocity of the gas through the carbon, etc. 

Concerning the influence of the humidity in the air and the 
carbon, the following results have been obtained 2 : 

Phosgene in contact with carbon is hydrolysed by moisture 
with formation of hydrochloric acid. 

The capacity for sorption at various phosgene concentrations, 
with dry carbon and dry air, follows Freundlich's equation. 

With dry carbon and air containing an excessive humidity it 
is found that the carbon contains a hydrolysing layer, a 
hydrochloric-acid-absorbing layer and a phosgene-absorbing 
layer. 

The time of resistance of the carbon increases up to a certain 
point with the moisture content of the carbon, since it dissolves 
the hydrochloric acid which forms. For small amounts of moisture 
the carbon layer first absorbs the hydrochloric acid, with high 
moisture content the phosgene first. 

Dry active carbon has protracted resistance if the air is high 
in humidity and low in phosgene concentration. 

The values of the sorptive powers for phosgene of activated 
carbon of various moisture-contents have been determined by 
Engelhardt. 3 

Materials which have been exposed to phosgene may be 
decontaminated by exposure to air and, if necessary, washing 
with a 10% solution of soda. 4 

The action of phosgene on foodstuffs differs according to 
whether foods of high water-content, like fresh meat, milk, beer, 
wine, etc., are being considered, or those poor in water like wheat, 
flour, coffee, etc. Those foodstuffs which are high in water- 
content absorb phosgene in large quantities and decompose it 
into hydrochloric acid and carbon dioxide. Fresh meat may 
remain edible according to the quantity of hydrochloric acid it 
contains. The drier foodstuffs can be made wholesome by 
exposure to a current of dry, warm air. 5 

1 H. Bunbury, /. Chem, Soc, 1922, 121, 1525. 

8 I. Nielsen, Z. ges. Schiess-Sprengstoffw., 1932, 27, 134-284. 

' Engelhardt, Z. Elektrochem., 1934, 40, 833. 

4 J. Thomann, Antigaz, 1935, 9, n. 3-4, 49. 

6 W. Plucker, Z. Untersuch. Lebensmitt., 1934, 3'7- 



74 



ACYL HALOGEN COMPOUNDS 



The absorption of phosgene by fats and its energetic action 
on the membranes of the lungs is attributed by Kling 1 to a 
possible reaction between the gas and the sterol existing in the 
fat of the lungs. In fact, phosgene reacts with cholesterol forming 
the chloroformic acid ester, which forms crystals melting at 
108 0 to no° C. 

According to the researches of Laqueur and Magnus, 2 the 
irritating power of phosgene on the mucous membranes and on 
the respiratory tract is very small, but the suffocating power 
great. 

The mortality-product, according to Meyer, 3 Hofmann 4 and 
others is 450. This value is, however, considered to be too low ; 
recent experiments 5 have demonstrated that it ranges for cats 
from 900 (Flury) to the figure (obtained by exposure to low 
concentrations of 5-7 mg. per cu. m.) of 3,000 (Wirth). This 
fact demonstrates, according to Wirth, that phosgene at very 
low concentrations behaves like substances of the hydrocyanic 
acid type with regard to mortality-product. According to 
American experiments, the mortality-product of phosgene is 
higher even than those already cited, and for dogs actually 
reaches 5,000 for an exposure time of 10 minutes. 6 

2. Carbonyl Bromide. COBr 2 . (M.Wt. 187 8) 

Carbonyl bromide, or bromophosgene, was prepared for the 
first time by Emmerling 7 by the oxidation of bromoform with 
potassium dichromate and sulphuric acid. Later it was also 
obtained by heating boron bromide to 150° C. with phosgene, 8 
but by this method a mixture with other compounds is obtained : 

2C0C1 2 + BBr 3 = COBr 2 + COClBr + BC1 3 . 

It is formed in small quantity also from carbon monoxide and 
bromine, in the presence of aluminium trichloride or by the action 
of the dark electric discharge 9 : 

CO + Br 2 = COBr 2 . 

The most suitable method for the preparation of carbonyl 
bromide consists in treating carbon tetrabromide with sulphuric 

1 A. Kling, Compt. rend., 1933, 197, 1782. 

2 Laqueur and Magnus, Z. ges. exp. Med., 1921, 13, 31. 

3 Meyer, Grundlagen des Luftschutzes , Leipzig, 1935, 61. 

* Hofmann, Sitzb. preuss. Akad. Wiss., 1934, 447- 

6 Flury, Gasschutz und Luftschutz, 1932, 149 ; Wirth, ibid., 1936, 250. 

6 Prentiss, Chemicals in War, New York, 1937. 

7 Emmerling, Ber., 1880, 13, 873. 

8 Besson, Compt. rend., 1895, 120, 191. 

* Bartal, Ann., 1906, 345, 334. 



CARBONYL BROMIDE 



75 



acid in a similar manner to Erdmann's preparation of phosgene 
(see p. 60). 

CBr 4 + S0 3 = COBr 2 + S0 2 Br 2 . 

Laboratory Preparation 1 

100 gm. carbon tetrabromide 2 are placed in a small flask 
fitted with a reflux condenser and warmed until it is completely 
melted. Then 90 ml. concentrated sulphuric acid (S.G. 1-83) 
are allowed to enter very slowly in drops, and the whole heated 
to 150 0 to 170 0 C. At the end of the reaction the mass is distilled, 
and the distillate, which is brown in colour because of the presence 
of bromine, is purified by addition of mercury in small portions, 
shaking and freezing. A further purification is effected by adding 
powdered antimony in small portions. It is distilled under 
reduced pressure in an all-glass apparatus with glass-to-glass 
connections. The product obtained is kept over antimony or 
silver powder in a sealed vessel. Yield 44%. 

Physical and Chemical Properties 

A colourless, heavy liquid of characteristic odour perceptible 
at great dilutions. It boils at ordinary pressure at 64° to 65° C, 
with incipient decomposition. 

Specific gravity about 2*5 at 15° C. 

Carbonyl bromide easily decomposes under the influence of 
light and heat, liberating bromine, according to the equation : 

COBr 2 = CO + Br 2 . 

This decomposition is accelerated by the presence of extraneous 
organic substances. 

It is hydrolysed by water : 

COBr 2 + H 2 0 = 2HBr + C0 2 . 

This reaction, according to Schumacher, takes place more 
slowly than in the case of phosgene. 

It reacts easily with bases, as, for example, with sodium 
hydroxide, to form sodium bromide and carbonate : 

COBr 2 + 4NaOH = 2NaBr + Na 2 C0 3 + 2H 2 0. 

With dimethylaniline in presence of aluminium tribromide, a 
coloured substance of the Crystal Violet type is formed. 

The vapour of carbonyl bromide attacks rubber, rendering it 
hard and brittle. 

Its physiopathological action is very similar to that of phosgene. 

'Schumacher, Ber., 1928, 61, 1671. 
2 A. Bartal, Chem. Ztg., 1905, 28, 377. 



7 6 



ACYL HALOGEN COMPOUNDS 



3. Chloroformoxime. 



(M.Wt. 79-4) 



>C = NOH. 



This substance was obtained for the first time by Nef 1 in 1894 
by the action of sodium fulminate on hydrochloric acid. It was 
prepared by Scholl 2 in a similar manner : 



Laboratory Preparation 

A solution of sodium fulminate cooled to o° C. is allowed to 
drop into 150 ml. of an aqueous solution of hydrochloric acid 
(1 part water and 1 of cone, hydrochloric acid) also at 0° C. It 
is immediately extracted three times with ether and distilled 



Physical and Chemical Properties 

It is obtained in the form of crystalline needles. Its odour is 
similar to that of hydrocyanic acid. 

It is stable at o° C, almost insoluble in petroleum ether, 
slightly soluble in carbon disulphide and easily soluble in other 
organic solvents and in water. The aqueous solution decomposes 
in time. 

Small quantities completely volatilise at the ordinary 
temperature. Large quantities decompose spontaneously with 
evolution of heat forming carbon monoxide and hydroxylamine 
hydrochloride (Nef). 

Treated for an hour with concentrated hydrochloric acid, it 
decomposes with quantitative formation of hydroxylamine. 

With silver nitrate it reacts according to the equation : 



An aqueous solution of chloroformoxime reacts with sodium 
hydrate and with ammonia, forming metafulminuric acid 3 ; 
treated with ferric chloride it gives an intense red coloration. 

It possesses lachrymatory and vesicant properties. 



CK 

C=NONa + 2 HQ = >C=NOH + NaCl 
H 



(Nef). 




C=NOH -+- 2 AgN0 3 = AgNO=C + AgCl + 2 HN0 3 



1 Nef, Ann., 1894, 280, 307. 
! Scholl, Ber., 1894, 27, 2819. 
8 Wieland, Ber., 1909, 42, 1350. 



DICHLOROFORMOXIME 



77 



4. Dichloroformoxime. (M.Wt. 113-9) 

CI 

>C = NOH. 
CK 

Dichloroformoxime, the oxime of carbonyl chloride, was 
prepared in 1929 by Prandtl and Sennewald 1 by the reduction 
of trichloro nitroso methane (see p. 164), with hydrogen sulphide 
according to the equation : 

CK 

CCI3NO + H 2 S = >C=NOH + S + HC1 
CY 

Instead of hydrogen sulphide, aluminium amalgam may be 
employed as reducing agent. 

Dichloroformoxime, like the corresponding dibromoformoxime, 
can also be prepared by treating fulminic acid with chlorine in 
the cold. 2 

Preparation from Trichloronitrosomethane (Prandtl) 

To a known quantity of trichloronitrosomethane is added a 
solution, saturated at ordinary temperature, of hydrogen sulphide 
in methyl alcohol (0-25 gm. HaS in 10 ml. alcohol at 15 0 C), 
10 ml. being added for each gramme of trichloronitrosomethane. 
The mixture is allowed to stand for several hours in a closed 
vessel until the blue colour of the nitroso compound disappears. 
If excessive heating takes place during this time, the vessel 
should be occasionally cooled by immersion in cold water. At 
the end of the reaction the product is treated with water and 
filtered from sulphur. It is then extracted with ether, dried over 
calcium chloride and distilled under reduced pressure. The 
oxime distils between 50° and 70 0 C. at 20 mm. of mercury. 

Preparation from Mercury Fulminate 3 

A current of chlorine is bubbled through a suspension of 
38 gm. mercury fulminate in 500 ml. semi-normal hydrochloric 
acid which is meanwhile stirred for 1 to 2 hours. The product is 
twice extracted with ether, the solvent evaporated and the oily 
residue distilled under reduced pressure. At a pressure of 15 mm. 
the distillation commences at 23 0 C, and after the first fraction 
has come over, the thermometer rises to 30 0 C. and dichloro- 
formoxime begins to crystallise in the condenser. This is then 
replaced by a receiver cooled in ice. Dichloroformoxine distils 
between 32 0 and 35 0 C. at 15 mm. Yield about 65%. 

1 Prandtl and Sennewald, Ber., 1929, 62, 1766. 

2 Birckenbach and Sennewald, Ann., 1931, 489, 18. 

3 G. Endres, Ber., 1932, 65, 67. 



78 



ACYL HALOGEN COMPOUNDS 



Physical and Chemical Properties 

Dichloroformoxime forms colourless, prismatic crystals melting 
at 39° to 40° C. Even at ordinary temperatures it has a high 
vapour pressure. It boils at normal pressure at 129° C. and at 
28 mm. of mercury at 53° to 54° C. It has a penetrating, 
unpleasant odour. 

It is a relatively stable substance, soluble in water and in the 
common organic solvents. Slow hydrolysis takes place in aqueous 
solution, according to the equation : 

Cl\ 

>C=NOH + 2 H„0 = C0 2 + HCl + NH 2 OH.HCl 

cr 

This hydrolysis is accelerated and becomes quantitative in 
presence of dilute acids. 

On raising to its boiling point under reflux, dichloroformoxime 
gradually decomposes to give brown vapours ; cyanogen chloride 
and hypochlorous acid are formed in the decomposition. 

The alkaline hydroxides and carbonates react energetically 
with an aqueous solution of dichloroformoxime, and heat is 
evolved, while the solution turns yellow. 

It reacts with ammonia even at the temperature of liquid air, 
forming ammonium chloride. By the action of aqueous ammonia 
on an ethereal solution of dichloroformoxime, cyanamide 
chloroformoxime is formed together with other products, 
according to the equation 1 : 

Ck CN-NH\ 
6 / )C=NOH + i4NH 3 = 3 / >C=NOH+ 9 NH 4 Cl+3 H 2 0+N s 

CI CI 

This substance forms colourless crystals melting at 168° C. ; 
it has no vesicant power. 

By the action of hydrazine on an aqueous solution of 
dichloroformoxime, hydrocyanic acid is formed by the following 
equation : 
CK 

2 ci/ )C=NOH + 2 N 2 H 4 = 2 HCN + 2 N 2 + 4 HCl + 2 H 2 0 

With fuming nitric acid it is transformed into dichlorodinitro- 
methane- 

ci )C-NOH^ ci )c(N0 2 ) 2 
a liquid boiling at 40° C at a pressure of 12 mm. 3 

1 Prandtl and Dollfus, Ber., 1932, 65, 755. 

8 Birckenbach and Sennewald, Ann., 1931, 489, 21. 

• R. Gotis and coll., /. Chem. Soc, 1924, 125, 442. 



OXALYL CHLORIDE 



79 



On treatment with copper acetate a small quantity of a tarry 
precipitate forms. Ferric chloride gives no colouration with 
dichloroformoxime, unlike chloroformoxime. 

Dichloroformoxime, even when stored in sealed vessels of 
glass or quartz, decomposes at ordinary temperatures with 
formation of phosgene and separation of a liquid compound. 
The decomposition is practically complete in 3-4 weeks, but is 
influenced by humidity and temperature. 1 The vapour of 
dichloroformoxime attacks rubber and cork. 

It has a violently irritant action on the mucous membrane 
of the nose and on the eyes. The vapour of this substance, even 
in very low concentrations, provokes lachrymation. 

When it comes into contact with the skin it produces 
inflammation and blisters, which can be prevented by treating 
the affected part immediately with plenty of aqueous ammonia 
(Prandtl). 

5. Oxalyl Chloride. (M.Wt. 126-9) 



Oxalyl chloride was prepared by Fauconnier 2 in 1892 by 
heating ethyl oxalate with phosphorus pentachloride. The 
product obtained in this way, however, is impure with phosphorus 
oxychloride. 

It is obtained in better yield and greater purity by the action 
of phosphorus pentachloride on oxalic acid : 



Preparation 3 

90 gm. anhydrous powdered oxalic acid are mixed with 400 gm. 
pulverised phosphorus pentachloride, cooling in ice. The mixture 
is allowed to stand for 2 or 3 days at the ordinary temperature 
until the mass is completely liquefied. It is then fractionally 
distilled ; the portion distilling between 6o° and 100° C. contains 
the oxalyl chloride. By repeated rectification it is obtained 
completely free from phosphorus oxychloride. Yield about 



CO— CI 





+ PA 



COC1 

j + POCl s + H 2 0 
COC1 



50%. 



1 Prandtl and Dollfus, Ber., 1932, 65, 758. 
a Fauconnier, Compt. rend., 1892, 114, 122. 
a Staudinger, Ber., 1908, 41, 3558. 



8o ACYL HALOGEN COMPOUNDS 



Physical and Chemical Properties 

A colourless liquid, boiling at 64° C. It solidifies on cooling 
to — 12° C. to a white crystalline mass, soluble in ether, 
chloroform, etc. 

In contact with water or alkaline solutions it decomposes 
quantitatively according to the equation : 

CO-C1 

I + H 2 0 = C0 2 + CO + 2 HCl 
CO-C1 

This reaction can be used for the quantitative determination 
of oxalyl chloride by measuring the volume of the carbon monoxide 
or by titrating the hydrochloric acid formed. 

Like other derivatives of oxalic acid, heating splits off carbon 
monoxide. By passing oxalyl chloride vapour through a tube 
1 m. long heated to 600° C. quantitative decomposition takes 
place : 

COC1 

I = CO + COCl 2 
COCl 

Oxalyl chloride decomposes in a similar manner when exposed 
to ultra-violet radiation 1 or when heated in carbon disulphide 
solution with aluminium chloride. 

It is stable to fuming sulphuric acid even when heated. 

Oxalyl chloride reacts with organic compounds in various 
ways : 

As an acid chloride, that is, retaining the grouping — CO — CO — , 
to form the corresponding ethers 2 from alcohols and the 
oxamides 3 from amines. 

Like phosgene, as in the decomposition by heat or in presence 
of aluminium chloride ; thus it reacts with dimethylaniline 
forming Crystal Violet. 4 

As chlorinating agent, it chlorinates aldehydes and ketones 5 
and reacts with acids in the cold, though better on heating, to 
form the acid chlorides, 6 etc. 

By passing oxalyl chloride vapour through a solution of aniline, 
oxanilide is obtained in quantitative yield (Staudinger). 

It does not react with zinc, mercury, silver or magnesium. 

Oxalyl chloride vapours strongly attack the respiratory organs. 

1 K. Krauskopf, /. Am. Chetn. Soc, 1936, 58, 443. 

8 Staudinger, Ber., 1908, 41, 3565. 

» Stoll6, Ber., 1913, 46, 3915. 

4 Postovsky, /. Khim. Promscl., 1927, 4, 552. 

* Staudinger, Bet., 1909, 42, 3966. 

• Ulich, /. Am. Chem. Soc, 1920, 42, 604. 



PHOSGENE : DETECTION 



81 



Analysis of the Acyl Halogen Compounds 

Detection of Phosgene 

Phosgene may be recognised by its odour. The minimum 
concentration detectable by odour is 4 mgm. per cu. m. of air, 
according to Suchier. 1 

By the use of chemical methods phosgene can also be detected 
by one of the usual tests for the hydrochloric acid formed by 
hydrolysis of the vapour. 

Following are the methods usually adopted for detecting 
phosgene : 

Method using Dimethyl Amino Benzaldehyde — Diphenylamine 
Paper. Phosgene, even if present in traces in the air, can be 
detected by means of papers prepared with dimethyl amino 
benzaldehyde and diphenylamine. 

These papers are prepared by immersing strips of filter paper 
in a solution of 5 gm. ^-dimethyl-amino-benzaldehyde and 5 gm. 
diphenylamine in 100 ml. ethyl alcohol and allowing them to dry 
in a dark place, or better still, according to Suchier, in an 
atmosphere of carbon dioxide. By exposing these papers, which 
are originally white or pale straw-yellow, to an atmosphere 
containing phosgene, an orange-yellow colouration is produced in 
a few seconds, the intensity of the colour varying with the 
concentration of phosgene. This change of colour is also observed 
in presence of chlorine or hydrochloric acid. 

It is possible to detect phosgene at a concentration of 4 mgm. 
per cu. m. of air. 2 

The test-papers should be kept in a closed container filled with 
carbon dioxide and protected from light, as it seems that the 
colour changes merely by the action of sunlight. 3 

Method using Nitroso-dimethylaminophenol Paper, Two 
solutions are prepared in xylene : 

(a) o-i gm. 1.3. 6-nitroso-dimethylaminophenol in 50 ml. 
xylene. 

{b) 0-25 gm. w-diethyl-aminophenol in 50 ml. xylene. 

5 ml. solution («) are mixed with 2 ml. solution (b) and strips 
of filter paper immersed in the mixture and allowed to dry. 4 
The paper should be damped with 50% alcohol just before use 
as the dry paper does not give the test. In the presence of 
phosgene the colour changes from white to green. 

1 Suchier, Z. anal. Chem., 1929, 79, 183. 

* This test-paper was employed by Dubinin (/. Prikl. Khim., 1931, 1109) to 
determine the duration of protection afforded by anti-gas niters against mixtures 
of air and phosgene. 

3 N. Kolobaiev, Khimija e Oborona., 1934, 10, 12. 

* Kretov, /. Prikl. Khim., 1929, 2, 483. 



82 ACYL HALOGEN COMPOUNDS 



These papers are specific for phosgene 1 and are more sensitive 
than the dimethyl amino benzaldehyde papers. Sensitivity : 
o-8 mgm. of phosgene per cu. m. of air. 2 

The two solutions (a) and (b) may be kept mixed for not more 
than 4 days. 

Kling and Schmutz's Method. 3 This method of detection 
depends on the ease with which the two chlorine atoms in phosgene 
react with the amino group of aniline : 

/CI /NHC 6 H 5 
CO( + 4 NH a C 6 H 5 -+CCK + 2 C 6 H 5 NH 2 . HC1 

N C1 X NHC„H S 

This leads to the formation of symmetrical diphenylurea in 
the form of rhombic prisms, 4 with a m.p. 236° C. This is insoluble 
in water. The reaction has the advantage of being specific for 
the CO group united to two chlorine atoms. 

In practice, in order to detect phosgene mixed with air or 
other inert gas by this method, it is sufficient to bubble the gas 
mixture under test through a few ml. of water saturated with 
aniline in the cold (3 gm. aniline in 100 ml. water). A white 
crystalline precipitate forms which can be easily seen, and, if 
necessary, confirmed by microscopic examination (rhombic 
prisms) or by a determination of the melting point (236 0 C). 

According to Kling, by passing 5 litres of a gas mixture 
(phosgene and air) through aniline solution at a velocity of about 
200 ml. a minute, it is possible to detect phosgene at a 
concentration of 40 mgm. per cu. m. of air. 5 

The sensitivity of this method of detection can be increased, 
according to Olsen, 6 by employing an aqueous solution of aniline 
saturated with diphenylurea. 

Detection of Phosgene in Presence of Halogens 

If the phosgene is mixed with halogens, e.g., chlorine or 
bromine, the latter may oxidise the aniline and so render the 
diphenylurea crystals impure. In this case it is necessary to 
pass the gas through a reagent which will remove them. This is 
carried out by inserting before the vessel containing the aniline 
a tube containing cotton wool soaked in a concentrated solution 

1 Pancenko, Metodi Issliedovanija i Khimiceskie Svoistva Otravliajuscik 
Vescestv, Moscow, 1934, 9 1 ; Studinger, Mitt. Lebensm. Hyg., 1936, 27, 12. 
a J. Thomann, Schweiz. Apoth. Ztg., 1937, '5, 41. 

3 Kling and Schmutz, Compt. rend., 1919, 168, 773. 

4 Mez, Zeit. Krist., 35, 254. 

6 This method was also recommended by Glaser and Frisch, Z. angew. Chem., 
1928, 41, 264. 

• Olsen and coll., Ind. Eng. Chem. Anal. Ed., 1931, 3, 189. 



PHOSGENE : DETERMINATION IN AIR 



83 



of potassium iodide and allowed to dry. In this way the chlorine 
and bromine deposit iodine which remains in the cotton wool, 
while the phosgene passes on unaltered. 

Quantitative Determination of Phosgene in Air 

Kling and Schmutz's Method. 1 This method depends on the 
reaction between phosgene and aniline, which has already been 
described. 

In order to carry out this determination, a volume of 1-5 litres 
of the gas mixture to be examined is passed through a bubbler 
containing water saturated with aniline. With gas mixtures 
containing more than 2% phosgene it is necessary to use a second 
bubbler to absorb any slight traces of phosgene which may escape 
the first. The precipitate which forms is collected on a small 
disc of filter paper supported on a spiral of platinum wire in the 
neck of a funnel. It is washed four or five times with the smallest 
possible amount of water in order to remove the aniline and then 
dried in an oven at 50 0 to 6o° C. for 2 hours so that the last traces 
of aniline are removed. 

If the precipitate is large enough to be weighed (more than 
10 mgm.), it is dissolved from the filter with boiling alcohol, 
collecting the nitrate in a tared platinum capsule. After 
evaporating the nitrate on a water bath, the residue is dried 
at 50° to 6o° C. for 2 hours and weighed. The quantity of 
phosgene present in the volume of air taken is obtained by 
multiplying the weight of the precipitate by 0-467. 

If, however, the precipitate of diphenylurea is too small to 
weigh accurately, it is converted to ammonia and determined 
colorimetrically by the Nessler method. In this procedure, the 
filter paper is removed from the funnel and placed in a small 
beaker ; 4 ml. pure sulphuric acid (66° Be) are added, allowing 
this to flow slowly over the platinum spiral and through the 
funnel so as to wash off all traces of adherent precipitate. To 
the mixture obtained in this way 10 mgm. mercuric sulphate are 
added and the whole is then kept near boiling temperature for 
2 hours. After allowing to cool, 20 ml. distilled water are added 
and the mixture is transferred to a 200-ml. flask containing 
0-25 gm. sodium thiosulphate dissolved in 100 ml. water to 
remove the mercury. The beaker is washed with water which is 
added to the contents of the flask until the total volume is about 
150 ml. and the ammonia determined in this. 

The authors recommend carrying out this determination in a 

1 A. Kling and R. Schmutz, Compt. rend., 1919, 168, 891. 



8 4 



ACYL HALOGEN COMPOUNDS 



small distillation apparatus (Aubin type) and liberating the 
ammonia by means of magnesium oxide. About 70 ml. liquid is 
distilled into 25 ml. water containing 1 ml. decinormal hydro- 
chloric acid. The distillate is then made up to 100 ml. and the 
ammonia determined in it by adding a few drops of recently 
prepared Nessler reagent. A solution of ammonium chloride 
containing 0-324 gm. NH 4 C1 per litre is used for comparison. 
1 ml. of this solution corresponds to 0-3 mgm. COCl 2 . 

This method of determination of phosgene with aniline gives 
results which are slightly low because the precipitate of 
diphenylurea is slightly soluble in water (5 mgm. in 100 ml. 
saturated aqueous aniline solution). According to Olsen, 1 more 
accurate results may be obtained by employing an aniline solution 
saturated with diphenylurea, prepared by passing phosgene into 
water saturated with aniline until a slight precipitate forms and 
filtering this off so as to obtain a clear liquid. 

According to Vies, 2 instead of determining the diphenylurea 
gravimetrically, the aniline hydrochloride formed in the filtrate 
may be titrated : 

C0C1 2 + 4C 6 H 5 NH 2 = CO(NHC 6 H 5 ) 2 + 2 C 6 H 5 NH 2 .HC1. 

Kling and Schmutz's Method, Modified by Yant. 3 A known 
volume of the gas mixture to be examined is passed through a 
solution of aniline prepared in the following manner : an excess 
of aniline is placed in water contained in a flask which is then 
stoppered, and, after shaking, allowed to stand for about a week, 
shaking two or three times a day. Then phosgene is bubbled 
through the solution until a permanent precipitate of diphenylurea 
is obtained. A portion of the reagent is filtered through a Gooch 
crucible just before the test when the titrate is ready for use. 

Analytical procedure : After passing the desired volume of the 
gas mixture through two absorption bottles in series containing 
the aniline solution, the latter is allowed to stand for 2 hours 
and then filtered through a weighed Gooch. The precipitate 
which remains in the bubbler tubes is washed out with hot 
alcohol. The alcoholic solution obtained is evaporated almost to 
dryness in a small beaker on the water bath, then a few ml. of 
water added and the evaporation continued until at last there is 
no longer any odour of alcohol. This solution is filtered through 
the same Gooch and the entire precipitate washed with normal 
hydrochloric acid saturated with pure diphenylurea. Air is 

1 Olsen, loc. cit. 

s S. Vles, Rec. trav. Chim., 1934, 53, 961. 

* Yant and coll., Ind. Eng. Chem., 1936, 28, 20. 



PHOSGENE : DETERMINATION IN AIR 



85 



drawn through the precipitate for a few minutes and then it is 
dried at 70° to 80° C. to constant weight. The precipitate is 
then dissolved from the crucible by washing several times with 
boiling ethyl alcohol, the alcoholic solution being evaporated 
and then dried in an oven at 70° to 8o° to constant weight. 
From this weight the quantity of phosgene in the gas mixture 
may be calculated. 

For determining phosgene in the atmosphere after extinction 
of a fire by means of an extinguisher of the carbon tetrachloride 
type, Yant 1 has proposed the apparatus shown in Fig. 4. The 

v wall of the 
5 qas-chamber 

r 



ft 



cotton 

wool-* - 

calcium^ 
chloride 



0 



spongy 
zinc 



spongy tin 
amalgamated tin 



to the * 

flowmeter 
or aspirator 



1 



bubbl 



ers 



cotto*n wool 



Fig. 4. 



sample to be examined is passed first through a purifier consisting 
of a U tube of 5 cm. diameter with one arm 22 cm. long and the 
other 30 cm. This tube is filled as follows : in the more constricted 
part between the two arms a little cotton wool is placed, and 
over this, in the short arm of the tube, a layer 12 cm. thick of 
calcium chloride in small granules while over this again is 6 cm. 
cotton wool In the long arm first a layer of spongy tin amalgam 
10 cm. thick, then a layer 3 cm. thick of spongy tin, and finally a 
15 cm. layer of zinc sponge, are introduced. 

The gas mixture is passed at a velocity of 1 litre a minute 
through two bubblers containing 25 ml. of an aqueous solution 
of aniline prepared as described on p. 84. 

Hydrochloric acid and chlorine do not interfere with the 
determination of phosgene by this method. 

1 Yant and coll., loc. cit. 



86 



ACYL HALOGEN COMPOUNDS 



Delepine, Douris and Ville's Method. 1 This method depends 
on the hydrolysis of phosgene by sodium hydroxide and the 
titration with silver nitrate of the hydrochloric acid formed. 

By means of an aspirator, a known volume of the gas mixture 
to be tested (2-5 litres in 4-10 minutes) is passed through 10 ml. 
of an aqueous alcoholic solution of soda prepared in the following 
way : 

Sodium hydroxide, normal solution . . 10 ml. 

95% alcohol 50 ml. 

Made up with water to 100 ml. 

After the passage of the gas the liquid is evaporated in a 
platinum (or porcelain) capsule on the water bath to a volume 
of 2-3 ml. and then 2 drops of acetic acid are added and the 
evaporation continued almost to dryness. The residue is 
redissolved in 2-3 ml. water and again evaporated to dryness to 
decompose the sodium biacetate which is formed. The residue 
is once more dissolved in 2 ml. water, a drop of potassium 
chr ornate solution added and then titrated with N/40 silver 
nitrate. It is advisable to carry out a blank determination. 
The amount of phosgene present in the sample is calculated from 
the number of ml. of N/40 silver nitrate solution employed in 
titration. 

This method can be improved, according to Matuszak, 2 by 
acidifying the alkaline solution with nitric acid and boiling in 
order to remove the carbon dioxide before neutralising and 
titrating. Also, according to the same author, in the case of the 
analysis of a gas mixture containing halogenated hydrocarbons, 
it is advisable to substitute an aqueous solution of sodium 
hydroxide. This absorbs the phosgene completely, is more stable 
and has the advantage of absorbing less of the halogenated 
hydrocarbons than the alcoholic solution. 

The Sodium Iodide Method. The determination of phosgene 
by this method, due to the Chemisch-Technischen Reichsanstalt, 3 
is carried out by titrating the iodine liberated when a gas mixture 
containing phosgene but free from acid gases, reacts with a 
solution of sodium iodide in acetone. The reaction is as follows : 
2NaI + COCljj = CO + I 2 + 2NaCl. 

The gas mixture to be examined is passed through a gas pipette 
(see Fig. 5) of about 500 ml. capacity until the air in bulb E is 
completely replaced by gas. Taps B and C are closed, the bulb D 
is completely freed from the gas mixture and 25 ml. of a 2% 

1 Delepine, Bull. soc. chim., 1920, [4] 27, 288. 

* M. Matuszak, Ind. Eng. Chem. Anal. Ed., 1934, 374- 

* Jahresb. der Chem. Tech. Reichsanstalt., 5, 1926, 11, 20. 



PHOSGENE ANALYSIS 



87 




solution of sodium iodide in acetone are introduced into it. The 
tap A is then closed and the sodium iodide solution allowed to 
run down into the bulb E after which the liberated iodine is 
titrated with N/10 or N/100 sodium thiosulphate 
solution in presence of starch paste. 

As the reaction between sodium iodide and 
phosgene proceeds quantitatively only in absence 
of water, the sodium iodide should be dissolved 
in acetone which has been dried for several 
days over calcium chloride. 

According to Matuszak 1 it is preferable to use 
potassium iodide rather than sodium iodide. (A 
saturated solution in acetone contains about 
1-9% of potassium iodide.) 

In order to determine phosgene in a gas 
mixture containing chlorine and hydrochloric 
acid by this method it is necessary to pass the 
gas mixture first through three U tubes. The 
first of these (that is, the one which the gas 
mixture first enters) contains calcium chloride, 
the second metallic antimony, and the third 
zinc dust. 2 

If K6lliker's 8 apparatus is used to determine 
phosgene in presence of hydrochloric acid, zinc 
dust cannot be used as it has too great a resist- 
ance. In this case the gas mixture to be tested 
is first passed through a wash bottle containing 
a sulphuric acid solution of silver sulphate (3 gm. 
in 100 ml. sulphuric acid of S.G. 1-84) and then through the 
acetone solution of sodium iodide. 



M 

Fig. 



Determination of Phosgene in Industrial Products 

About 0-2 to 0-3 gm. phosgene is accurately weighed 4 in a glass 
bulb sealed in the flame. This bulb is then introduced into a 
bottle of 250 ml. capacity in which 150 ml. of an aqueous solution 
of aniline have previously been placed (26 gm. aniline in 1 litre 
of water). 

The bottle is tightly closed and shaken so as to break 
the bulb. A flocculent white precipitate of diphenylurea forms 
immediately. After allowing to stand for 2 hours, the liquid is 

1 M. Matuszak, Ind. Eng. Chem. Anal. Ed., 1934. 457- 

a Bielasky, Z. angew. Chem., 1934, 47, 149. 

3 K6ixiker, Die Chemische Fabrtk., 1932, 5, 1 ; 1933, 6, 299. 

* Kling and Schmutz, Co'mpt. rend., 1919, 168, 774. 



88 



ACYL HALOGEN COMPOUNDS 



filtered through a Gooch crucible, preventing the broken pieces 
of the bulb from entering the crucible as far as possible, washed 
with 50-60 ml. cold water, dried at 70 0 C. and weighed. 

As this precipitate always contains some fragments of glass 
it is advisable to redissolve the diphenylurea from the crucible 
with boiling acetone, then drying the crucible in an oven, heating 
it to 400° C. and reweighing. The difference between the two 
weights, multiplied by 0-467, gives the weight of phosgene 
contained in the gas sample employed. 

It should be noted that the reaction between phosgene and 
aniline takes place only in presence of an excess of the latter. 

Determination of Free Chlorine in Phosgene 

In the synthetic preparation of phosgene from chlorine and 
carbon monoxide, some free chlorine may remain dissolved in 
the phosgene. 

Various methods have been suggested for the determination 
of free chlorine in phosgene. The most commonly used method is 
that of Delepine, 1 in which 500 ml. dilute sodium hydroxide 
solution are placed in a vessel closed with a ground-glass stopper, 
and a glass bulb containing a weighed quantity of the phosgene 
to be tested is dropped in. The bulb is broken, and after a few 
minutes an alkaline solution of sodium iodide is added and the 
liquid acidified. If the phosgene contains any free chlorine, this 
liberates an equivalent quantity of iodine which is titrated with 
thiosulphate solution. 2 

Recently Nenitzescu 3 has described another method which 
allows the simultaneous determination of chlorine and phosgene. 
It is based on the separation of chlorine from phosgene by passage 
of the mixed gas through metallic antimony and absorption of 
the phosgene by an alcoholic potash solution. 

The mixture to be examined is passed through a U tube filled 
with metallic antimony and previously weighed (about 20 gm.). 
The antimony absorbs the chlorine quantitatively without 
reacting with the phosgene. The residual gas is passed into a 
Fresenius potash bulb containing 20 ml. 10% alcoholic potash, 
and connected by glass to glass joints with the U tube. The 
bulb tube of the Fresenius potash bulb is connected with a tube 
filled with silica gel to catch solvent vapour. The absorption of 
phosgene in the alcoholic solution of potash is complete. In order 

1 Dblepine, Bull. soc. chim,, loc. cit. 

5 This method was also recommended by A. E. Kretov, /. Prikl. Khim., 
1929, 2, 483. 

3 Nenitzescu and Pana, Bull. soc. chim. Rom., 1933, 15, 45. 



PHOSGENE : DETERMINATION OF HCl 89 



to displace all the phosgene from the apparatus a current of dry 
air is passed through at the end of the test. 

The difference in the weights of the antimony U tube before and 
after the absorption gives the amount of chlorine present in the 
gas mixture. 

The difference in the weights of the potash bulb and the silica 
gel before and after the absorption gives the amount of phosgene 
in the sample. 

Determination of Hydrochloric Acid in Phosgene 

In the synthetic preparation of phosgene, if the carbon 
monoxide is not perfectly dry or contains a trace of hydrogen, 
hydrochloric acid will be formed and will remain dissolved in the 
phosgene. 

If this acid is present in considerable quantity, it may be 
determined quantitatively by the gas-volumetric method of 
Berthelot, 1 which consists in absorbing the hydrochloric acid in a 
small quantity of water. Measurement of the volume of the 
phosgene before and after the treatment with water gives the 
quantity of hydrochloric acid present in the sample. In this 
determination the hydrolysing action of the water on the phosgene 
may be neglected, for the small quantity of phosgene hydrolysed 
produces an equal volume of carbon dioxide. 

COCl 2 + H 2 0 = 2HCI + C0 2 . 

It is, of course, obvious that this method cannot be employed 
for the determination of small amounts of hydrochloric acid in 
phosgene. 

In this case, use is made of the property of very dilute, gaseous 
hydrochloric acid of reacting with mercuric cyanide, liberating 
an equivalent quantity of hydrocyanic acid, while phosgene does 
not do this. 2 

Delepine and Monnot 3 have worked out the following method 
from this difference in behaviour 4 : 

5 gm. powdered mercuric cyanide and a glass bulb containing 
the phosgene are placed in a perfectly dry flask of 500-1,000 ml. 
capacity which is closed by a ground-glass stopper carrying two 
tubes, one leading to the bottom of the flask and the other 
projecting only a few cm. inside. The flask is evacuated by 
means of a mercury pump, the glass bulb is broken and the whole 
allowed to stand for 12-14 hours. At the end of this period, a 

1 Berthelot, Bull. soc. chim., 1870, [2] 13, 15. 
8 Berthelot and Gaudechon, Compt. rend., 1913, 156, 199°- 
3 Delepine and Monnot, Bull. soc. chim., 1920, [4] 27, 292. 
* This method was also recommended by Kretov, loc. cit. 



go ACYL HALOGEN COMPOUNDS 



vessel containing about 50 ml. 2 N. sodium hydroxide solution 
is connected between the pump and the flask, while the other 
tube from the flask is connected with a wash-bottle containing 
concentrated sulphuric acid. Dry air is slowly allowed to enter 
the flask to bring the pressure to atmospheric and then a current 
of air drawn through the whole apparatus at a speed of about 
twenty-five bubbles a minute for 8-9 hours. In this way the hydro- 
cyanic acid and the phosgene are swept out in the air stream and 
bubbled through the alkaline solution which completely absorbs 
them. 

At the end of the operation, 5 ml. of ammonia are added to the 
alkaline solution and 1 ml. 10% sodium iodide solution, after 
which the hydrocyanic acid present is titrated with N/20 silver 
nitrate solution. The number of ml. of silver nitrate employed, 
multiplied by 0-00365 gives the amount of hydrochloric acid 
present in the sample of phosgene employed. 



CHAPTER VII 



HALOGENATED ETHERS 



The war gases belonging to this group may be considered as 
true ethers whose alkyl groups have a hydrogen substituted by a 
halogen atom. 

These compounds are usually prepared by the direct action of 
the halogens on the corresponding ethers. For example, from 
methyl ether and chlorine, dichloromethyl ether is obtained 1 : 



However, in the particular case of the halogenated methyl 
ethers it is preferable, especially in their industrial manufacture, 
to commence with formaldehyde (or its polymers) and the 
hydrogen halide. In this case the reaction takes place in two 
stages ; for instance, in the preparation of dichloromethyl ether, 
chloromethyl alcohol is formed first : 



and then this in the presence of dehydrating agents is transformed 
into symmetrical dichloromethyl ether : 



The compounds of this group furnish a typical example of the 
influence exercised by the symmetry of the molecular structure 
on the aggressive power of the substances. It has been found 
experimentally that while the symmetrical ethers 



have a powerful irritant effect, the asymmetric ethers, which 
contain the same number of halogen atoms in the molecule 




CH 2 0 + HC1 — CI — CH 2 OH, 



2 Cl-CH 2 OH -*H 2 0 + 0( ' 

N CH 2 C1 




and 





and 




1 Moreschi, Atti accad. Lincei., 28 (I), 277. 
91 



9 2 



HALOGEN ATED ETHERS 



have no offensive properties whatever. Dichloromethyl and 
dibromomethyl ethers were used as war gases in the war of 
1914-18, especially by the Germans. 

These substances have a high mortality-product, but very low 
irritant power. According to some workers, they act on the 
semicircular canals and produce staggering and vertigo ; they 
have been, therefore, named " labyrinthic gases." They have 
had little success, however, more particularly because of their 
great sensitivity to the hydrolysing action of water. 

Since the war various higher homologues of dichloromethyl 
ether have been prepared and studied from the point of view of 
their offensive power. Among these, symmetrical dichloroethyl 
ether 1 may be mentioned : 

/CH 2 -CH 2 C1 
N CH 2 -CH 2 C1 

This has a structure analogous to dichloroethyl thioether, or 
mustard gas, which has the formula : 

/CH 2 -CH 2 -C1 
' ^CH 2 -CH 2 -C1 

Dichloroethyl ether, though very similar in its chemical 
properties to the sulphur derivative, has very different physio- 
pathological properties, being destitute of vesicant power. 2 
According to Hofmann 3 this lack of vesicant power must be 
attributed to the fact that dichloroethyl ether, unlike dichloroethyl 
sulphide, cannot penetrate the epidermis. 

1. Dichloromethyl Ether (M.Wt. 11476) 

/CH 2 C1 

N CH 2 C1 

Dichloromethyl ether is employed in war both as a war gas and 

as a solvent for other war gases (ethyl dichloroarsine, dichloroethyl 

sulphide, etc.). It was obtained for the first time by Regnault 4 

who brought about the reaction between methyl ether and chlorine 

by means of diffused sunlight. It is better prepared, however, 

by the action of hydrochloric acid on trioxymethylene 5 : 

2(CH 2 0) 3 + 6HC1 = 3H 2 0 + 3C1CH 2 — 0— CH 2 C1. 

1 Kamm and Valdo, /. Am. Chem. Soc, 1921, 43, 2223. 

a Cretcher and Pittenger, /. Am. Chem. Soc, 1925, 47, 1173. 

3 Hofmann, Sitzb. preuss. Ahad. Wiss., 1934, 447. 

* Regnault, Ann., 1, 292 (3rd edn.). 

6 Tiscenko, /. Rusk. Fis. Khim. Ob., 1887, 19, 473 ; Grassi and Maselli, 
Gazz. Chim. Hal., 1898, 28 (II), 477 ; Litterscheid, Ann., 1904, 334, 1. 



DICHLOROMETHYL ETHER : PREPARATION 93 



The water produced in this reaction causes the gradual 
decomposition of the ether as it is formed, and for this reason, 
chlorosulphonic acid 1 is used to replace the hydrochloric acid. 
The reaction is then as follows : 

/CI /OCH 2 Cl 
CH 2 0 + SO a ( = S0 2 ( 

/OCH 2 Cl /CH 2 C1 
2 S0 2 ( 0( 4- H 2 S0 4 + S0 3 

X OH N CH 2 C1 

It is also obtained by passing the vapour of monochloroacetic 
acid through a red-hot tube 2 : 

CH 2 C1 /CH.C1 
1 -* 0< + H„0 + 2 CO 

COOH N CH 2 C1 



2 



and also by the action of phosphorus trichloride on trioxy- 
methylene in presence of zinc chloride. 3 

Laboratory Preparation 4 

30 gm. paraformaldehyde and 40 gm. 80% sulphuric acid 
(S.G. 173) are weighed accurately into a flask of about 200 ml. 
capacity, which is closed by a two-holed stopper. Through one 
of the holes in the stopper a tap-funnel passes, and through the 
other a glass tube to lead the gas formed in the reaction to an 
aspirator. While agitating and cooling to o° C. by means of a 
freezing mixture, 175 gm. chlorosulphonic acid are added drop by 
drop from the tap-funnel, care being taken that the temperature 
does not rise above 10° C. At the end of the reaction (1-2 hours) 
the product is poured into a dry separatory funnel, the upper 
oily layer separated and washed with dilute sodium carbonate, 
and finally distilled at normal pressure. Yield 80-90%. 

Industrial Manufacture 

In Germany, 5 this ether was manufactured by the same 
method as that described above for the laboratory preparation : 
by the action of chlorosulphonic acid on formaldehyde. The 
reaction is carried out in iron vessels of 5 cu. m. capacity (about 
1,100 gals.), coated internally with acid-resistant material and 
fitted with stirring apparatus and lead cooling coils. 

1 Fuchs and Katscher, Ber., 1927, 60, 2288. 

2 Grassi and Cristaldi, Gazz. Chtm. Hal., 1897, 27 (II), 502. 

3 Descude, Bull. soc. chim , 1906, 35, 198. 
* Stephen, /. Chem. Soc, 1920, 117, 510. 

5 Norris, /. Ind. Eng. Chem., 1919. 11, 819. 



94 



HALOGEN ATED ETHERS 



1,200 kg. 70% sulphuric acid are first placed in the vessel and 
then 600 kg. paraformaldehyde added, continuous agitation 
being maintained and the temperature being kept at 5 0 to 10° C. 
The operation takes between 3 and 4 hours. Then 2,400 kg. 
chlorosulphonic acid are added very slowly (in about 48 hours), 
the agitation being continued and the temperature kept between 
10° and 15° C. At the end of the reaction the liquid forms two 
layers, the lower consisting of sulphuric acid and the upper the 
ether. Yield 90-95%. 

Physical and Chemical Properties 

Dichloromethyl ether is a colourless liquid, boiling at 105° C. 
at ordinary pressure, and at 46° C. at 100 mm. mercury. The 
specific gravity is 1-315 at 20° C. The volatility is fairly high ; 
at 20° C. it is 180,000 mgm. per cu. m. The density in the gaseous 
state is 3-9. 

It is insoluble in water, but dissolves in methyl and ethyl 
alcohols with evolution of heat. It is also soluble in acetone and 
in benzene (Tiscenko) . 

Heat decomposes it into hydrochloric acid and trioxymethylene. 
With water it forms formaldehyde and hydrochloric acid, even 
at ordinary temperatures 1 : 



The hydrolysis of 1 gm. of dichloromethyl ether, dissolved in 
ethyl ether in contact with 250 ml. water and agitated, is complete 
in 95 minutes. 2 

Even atmospheric humidity causes this decomposition. Alkalies 
and carbonates react with dichloromethyl ether forming the 
chloride of the metal and formaldehyde. Ammonia, however, 
forms hexamethylene tetramine, 3 



3 °\„ ™ + 10 NH 3 = (CH 2 ) 6 N 4 + 6 NH 4 C1 + 3 H a O, 



identifiable by its reaction with bromine water to give a 
yellow, crystalline substance which is a bromo-derivative of 
hexamethylene tetramine. 

Dichloromethyl ether is converted by chlorine under the action 
of sunlight 4 into : 

1 Sonay, Bull. acad. toy. belg., 1894, [3] 26, 629 ; Ber., 1894, 27, 336 ; 
Litterscheid, Ann., 1901/3I6, 177. 

2 Straus, Ber., 1909, 42, 2168 ; Straus and Thiel, Ann., 1936, 525, 161. 
» Brochet, Ann. chim. phys., 1897, [7] 10, 299. 

* Sonay, Bull. acad. roy. belg., 1894, [3] 26, 629. 




CH 2 C1 
CH,C1 





CH.C1 



DICHLOROMETHYL ETHER: PROPERTIES 95 

(1) Trichloromethyl ether : a lachrymatory liquid with a 
pungent odour, boiling at 130 0 to 132° C. Density, 1-5066 at 
10° C. Insoluble in water, soluble in alcohol, ether, benzene, 
carbon disulphide. 

(2) T etrachloromethyl ether : a liquid which fumes in air and 
has a more pungent odour than the preceding compound. B.p. 
I45°C. and density 1-6537 a t 18 0 C. Unlike trichloromethyl 
ether, it is insoluble in alcohol, ether, benzene and carbon 
disulphide. By long boiling with water it decomposes into formic 
acid and crystals of hexachloroethane. 

When exposed to ultra-violet rays and heated to about 8o° C, 
the chlorination of dichloromethyl ether proceeds differently and 
pentachloromethyl ether is formed. 1 



This is a colourless liquid with an odour of phosgene and 
b.p. 158-5° to 159*5° C. Density 1-64 at 20° C. It is stable to 
cold water, but on heating with water it decomposes to form 
hexachloroethane, hydrochloric acid, carbon monoxide and 
carbon dioxide. With an aqueous solution of aniline it forms 
diphenyl urea. 

Further chlorination causes the substitution of all the six 
hydrogen atoms by chlorine and hexachloromethyl ether is 
obtained. This is a liquid with an odour of phosgene, having a 
boiling point of 98° C, at which temperature it partially decom- 
poses into phosgene and carbon tetrachloride. Density 1*538 
at 18° C. 

By bubbling a current of sulphur trioxide through dichloro- 
methyl ether cooled in ice and salt, besides monochloromethyl 
chlorosulphonate, dichloromethyl sulphate is formed as follows 2 : 



Dichloromethyl sulphate is a colourless, odourless liquid with 
b.p. 96° to 97° C. at 14 mm. of mercury and density i-6o at 
ordinary temperatures. It is readily soluble in the common 
organic solvents, though only slightly in petroleum ether. Unlike 
dimethyl sulphate, it has no physiopathological action. 

1 Rabcewicz and Chwalinsky, Roczniki Chem., 1930, 10, 686. 
a Fucns and Katscher, Ber., 1927, 60, 2295. 





9 6 



HALOGEN ATED ETHERS 



Boiling with sodium methylate converts dichloromethyl ether 
into dimethyl methylal. 1 The reaction apparently takes place in 
two phases : dimethoxy methyl ether is first formed, 

/CH 2 C1 /CH 2 OCH 3 
0< +2 NaOCH 3 = 2 NaCl + 0< 

X CH 2 C1 N CH 2 OCH, 

and then this in presence of excess alcohol is decomposed into 
water and dimethyl methylal : 

/CH 2 OCH 3 /OCH 3 
0< +2 CH3OH = H 2 0 + 2 CH 2 < 

N CH 2 OCH 3 N OCH 3 

In the presence of dehydrating agents such as zinc chloride, 
dichloromethyl ether reacts with benzene to form benzyl 
chloride : 

/CH 2 C1 

°L + 2 C 6 H 6 = 2 C 6 H 5 -CH 2 C1 + H 2 0 
LH 2 L1 w 

In the absence of moisture most metals are unattacked by 

dichloromethyl ether. 
It finds application in the refining of lubricating oils. 2 
The lower limit of irritation, that is, the minimum concentration 

which produces lachrymation, is 14 mgm. per cu. m. The limit 

of insupportability is 40 mgm. per cu. m. The product of 

mortality is 500 (Miiller). 

2. Dibromomethyl Ether (M.Wt. 204) 

/CH 2 Br 

N CH s Br 

Like the preceding substance, dibromomethyl ether found a 
very limited application in the war of 1914-18. It was used both 
as a war gas and as a solvent for the chloroarsines. 

It is easily obtained by the reaction of trioxymethylene with 
hydrobromic acid. 3 

Laboratory Preparation 4 

30 gm. paraformaldehyde are mixed with 80 gm. sulphuric acid 
(S.G. 1-84) in a 300-ml. flask. The mixture is cooled in ice and 

1 Sonay, he. cit. ; Litterscheid and Thimme, Ann., 1904, 334, 13. 

2 French Pat. 748925/1933. 

8 Tischenko, /. Rusk. Fis. Khim. Ob., 1914, 46, 705. 
4 Stephen, /. Chem. Soc, 1920, 117, 510. 



DIBROMOMETHYL ETHER 



97 



agitated continuously while 155 gm. finely powdered sodium 
bromide are added in small portions. By heating at the boiling 
point for 10 minutes, the paraformaldehyde dissolves and an 
oily layer of dibromomethyl ether floats to the top. This is 
separated and purified by distillation. 

Industrial Manufacture 1 

Six parts by weight of 70% sulphuric acid and 1 part of 
paraformaldehyde are placed in an acid-resistant vessel, the 
mixture stirred and cooled so as to keep the internal temperature 
at 15° to 20 0 C, and then ammonium bromide added slowly in 
amount about 10% in excess of that calculated. At the end of 
this operation, which requires about 48 hours, the mass is stirred 
for a further 5-10 hours at 30° C. and then the dichloromethyl 
ether separated. Yield 70-80%. 

Physical and Chemical Properties 

Dibromomethyl ether is a colourless liquid boiling at 154° to 
155° C. and solidifying at — 34° C. 2 Its specific gravity is very 
high (2-2) and its volatility at 20° C. is 21,100 mgm. per cu. m. 
It has a coefficient of expansion of 0-0009. Though insoluble in 
cold water, it dissolves easily in ether, benzene and acetone. 

Water decomposes dibromomethyl ether with formation of 
hydrobromic acid and formaldehyde, according to the equation 3 : 



This decomposition takes place more rapidly in the presence of 
alkaline solutions (Tiscenko). 

By heating with trioxymethylene and water to 140 0 , methyl 
bromide and formic acid are formed. It reacts energetically with 
alcohols and phenols, but is not attacked at ordinary temperatures 
by concentrated sulphuric acid (Henry). 

The minimum concentration capable of provoking lachrymation 
is 20 mgm. per cu. m. of air. The limit of insupportability is 
50 mgm. per cu. m., and the product of mortality is 400, which 
is greater than that of phosgene (Muller). 

1 Norris, loc. cit. 

a Henry, Bull, acad, roy. belg. 1894, [3] 26, 615 ; Ber., 1894, 27, 336. 
s P. Rona, Z.ges. exp. Med., 1921, 13, 16. 

WAR cases. 4 




'CH 8 Br H- 
CH 2 Br + H' 




9 8 



HALOGEN ATED ETHERS 



Analysis of the Halogenated Ethers 

Quantitative Determination of Dichloromethyl Ether 

The ether is decomposed by water and the formaldehyde 
obtained is titrated iodometrically : 

/CH 2 C1 

0< + H 2 0 = 2 HC1 + 2 CH.0 

X CH 2 C1 

CH 2 0 + I 2 + 3 NaOH = HCOONa + 2 Nal + 2 H,0 

0-1-0-15 gm. of the substance to be examined is weighed into 
a glass bulb which is then placed in a flask containing ioo ml. 
water. After closing the flask with a stopper the bulb is broken, 
and the whole allowed to stand for 2-3 hours. 40 ml. N/10 iodine 
solution are added from a burette and then an aqueous solution 
of sodium hydroxide until the liquid is a clear yellow in colour. 
After allowing to stand for 15-20 minutes, 2 N hydrochloric acid 
is added to acidify and to liberate the iodine, and excess of the 
latter is then titrated with decinormal sodium thiosulphate in 
presence of starch. 

1 ml. N/10 iodine solution corresponds to 0-002874 gm. 
dichloromethyl ether. 



CHAPTER VIII 
HALOGENATED ESTERS OF ORGANIC ACIDS 
(A) THE METHYL FORMATE GROUP 

These compounds form an important group of war gases. 
They were employed alone and also mixed with other war gases : 
phosgene, chloropicrin, diphenyl-chloroarsine, etc. 

Structurally, these compounds may be considered as derivatives 
of methyl chloroformate : 

CI 



i 



OOCH3 

by the substitution of successive hydrogen atoms of the methyl 
group by chlorine atoms : 

CI CI CI 

COOCH 2 Cl COOCHCl 2 COOCCl 3 

monochloro methyl dichloro meth) 1 trichloro methyl 

chloroformate chloroformate chloroformate 

or else as derivatives of the methyl ester of monochlorocarbonic 
acid : 

/OCH 3 
OC< 
X C1 

by the progressive substitution of the hydrogen atoms of the 
methyl group by chlorine atoms. 

They may be prepared by two different methods : 

(1) From Methyl Formate. 1 By chlorination of methyl 
formate, obtained from methyl alcohol and formic acid according 
to the equation : 

CH3OH + HCOOH = HCOOCH3 + H 2 0. 

(2) From Methyl Chloroformate. 2 By chlorination of methyl 
chloroformate, obtained from methyl alcohol and phosgene. 

CHgOH + COCl 2 = CICOOCH3 + HC1. 

The compounds of this group have a characteristic penetrating 

1 Hentschel, /. prakt Chem., 1887, 36, 99. 

2 Kling and coll., Compt. rend., 1919, 169, 1046. 



ioo HALOGEN ATED ESTERS OF ORGANIC ACIDS 



odour and also lachrymatory and asphyxiating properties. It is 
noteworthy that as the number of chlorine atoms in the methyl 
group increases, the lachrymatory power diminishes and the toxic 
and asphyxiating power increases. For example, while the first 
member of the series, monochloromethyl chloroformate, has an 
essentially irritant action, the last member, trichloromethyl 
chloroformate, is essentially toxic and asphyxiating, its 
lachrymatory action being weak. 

Since the war other analogous compounds have been studied, 
especially from the physiopathological point of view. Such are 
methyl cyanoformate 1 and ethyl cyanoformate, which are 
powerful lachrymators but are easily decomposed by the action 
of water. 

Recently some fluorine derivatives have also been prepared 2 : 
Methyl fluoroformate, obtained by the action of thallium fluoride 

on methyl chloroformate, is a liquid boiling at 40 0 C. Density 

i-o6at 3 3°C. 

Ethyl fluoroformate, obtained by the action of thallium fluoride 
on ethyl chloroformate, is a liquid with b.p. 57° C. and density i-n 



Methyl formate was prepared in 1835 by Dumas 3 by the action 
of dimethyl sulphate on sodium formate. Later, it was obtained in 
better yield by the reaction between magnesium or aluminium 
methylate and trioxymethylene. 4 

It is usually prepared, however, by the action of methyl alcohol 
saturated with hydrochloric acid on calcium formate 6 : 

(H.COO) 2 Ca + 2CH3OH = 2HCOOCH3 + Ca(OH) 2 . 

Laboratory Preparation 5 

100 gm. calcium formate are placed in a flask fitted with a 
tap-funnel and a reflux condenser, the latter being connected 
with a well-cooled descending condenser. 130 ml. methyl alcohol 
recently saturated with hydrochloric acid (that is, containing 

1 Weddige, /. prakt. Chem., 1874, 10, 197. 

2 H. Goswami and Sarkar, /. Indian Chem. Soc, 1933, 10, 537. 

3 Dumas, Ann., 1835, 15, 35. 

4 Tischenko, /. Rusk. Fis. Khim. Ob., 1906, 38, 355 ; Chem. Zentr., 1906 
(II), 1309. 

6 Volhard, Ann., 1875, 176, 133. 




(M.Wt. 60) 



METHYL FORMATE : METHYL CHLOROFORM ATE 101 



about 40% HC1) are placed in the tap-funnel and allowed to flow 
slowly on to the calcium formate, shaking at intervals. When 
all the alcohol has been added, the mixture is allowed to stand 
for a short time and then distilled from a water-bath. The 
distillate is washed many times in a tap-funnel with a little 
saturated sodium chloride solution, neutralising with sodium 
carbonate. In order to separate water formed in the reaction 
and the excess methyl alcohol, the product is placed in a flask 
fitted with a reflux condenser and allowed to stand with a large 
quantity of fused and finely ground calcium chloride for 24 hours. 
The methyl formate and calcium chloride form a crystalline 
compound, and when this is distilled on a water-bath pure 
methyl formate comes over. 

Industrial Manufacture 

95% formic acid and methyl alcohol without any condensing 
agent are placed in an iron still,- coated internally with acid- 
resistant material and fitted with copper coils, and heated. 
The product obtained is distilled and the distillate then redistilled. 

Physical and Chemical Properties 

Methyl formate is a liquid boiling at 317° C. at 760 mm. 
pressure. It has a S.G. of 0-9745 at 20° C. and on cooling in 
liquid air solidifies at — ioo° C. 

Water or alkaline solutions saponify it. The velocity of this 
decomposition has been determined in the presence of various 
saponifying agents. 1 

By exposure to ultra-violet light it decomposes, forming carbon 
dioxide, hydrogen and methane. 2 

Chlorine aided by sunlight transforms it into various chlorine 
derivatives : mono-, di and trichloromethyl chloroformates (see 
p. 104). 

It has been used as a solvent for cellulose acetate. In chemical 
warfare it is interesting as an intermediate for the manufacture of 
its chloro- derivatives. 

2. Methyl Chloroformate (M.Wt. 94 5) 



This compound may be obtained by directly chlorinating 

1 Holmes, /. Am. Chem. Soc, 1916, 38, no ; Skrabal, Monatsh., 1917. 38, 
191. 

s Berthelot, Compt. rend., 1911, 153, 384. 




102 HALOGEN ATED ESTERS OF ORGANIC ACIDS 



methyl formate, but it is more commonly prepared from the 
reaction between phosgene and methyl alcohol 1 : 



N C1 

During this reaction it is necessary to keep the temperature 
rather low and to be careful to maintain the phosgene always in 
excess. This is in order to prevent the following reaction from 
taking place and methyl carbonate from being formed : 

/OCH 3 

C0C1, + 2 CH3OH = C0< + 2 HC1 

X OCH 3 

This is a colourless liquid, boiling at normal pressure at 90-6° C. 
M.p. 0-5° C. Density at 17° C. is 1-065. Insoluble in water ; 
soluble in alcohol, ether, etc. Its aggressive power is less than 
that of methyl cElofc5forma£e. By chicrmation, hexachloromethyl 
carbonate i& ■formed, also known as "- irpphssgene " (see p. 115). 

Laboratory Preparation a 

A small quantity, about 10 ml., of methyl chloroformate is 
placed in a flask fitted with a tap-funnel, a tube to introduce the 
phosgene and an exit tube, and after cooling to 0° C. a current 
of chlorine-free phosgene is bubbled in. Methyl alcohol is added 
from the tap-funnel, after a time, in volume about one-third of 
that of the liquid in the flask, this addition being made all at once. 
The addition of a fresh quantity of methyl alcohol is made when 
it is obvious that the phosgene is no longer being absorbed. The 
total quantity of methanol used should preferably not exceed 
150 ml. 

As soon as the reaction is complete, the product is transferred 
to a separatory funnel containing cold water. The oily, colourless, 
heavy layer which separates from the aqueous layer is washed 
twice with cold water, dried over calcium chloride and fractionally 
distilled from a water-bath. The fraction passing over between 
69° and 72 0 C. is collected. Yield about 70% of theory. 3 

Industrial Manufacture 

In the French method the reaction between methanol and 
phosgene takes place in large vessels fitted with agitators and 
cooled externally. The hydrochloric acid which forms is rapidly 




1 Dumas, Ann., 1835, 15, 39. 

2 Klepl, /. prakt. Chem., 1882, 26, 448 ; Hentschel, Ber., 1885, 18, 1177. 
8 Stolzenberg, Darstellungsvorschriften fur Ultragifte, Hamburg, 1930, 42.' 



METHYL CHLOROFORM ATE : PROPERTIES 103 



removed either by bubbling a stream of indifferent gas through the 
liquid, or by adding calcium carbonate. 

In the German plants, however, methyl chloroformate was 
made by first introducing into the reaction vessels, which were 
of cast iron lined internally with lead and of about 3 cu. m. 
capacity (about 660 gallons), a small quantity of the ester and 
then liquid phosgene and anhydrous methanol in small portions, 
with stirring. The temperature was regulated during the reaction 
so that it did not rise above o° C. Yield about 80% of theory. 

Physical and Chemical Properties 

Methyl chloroformate is a clear liquid which boils at ordinary 
pressure at 71-4° C. The specific gravity at 15 0 C. is 1-23 ; the 
vapour density is 3-9 (air = 1). 

It is fairly stable to cold water, 1 but is decomposed by hot 
water to form methanol, hydrochloric acid and carbon dioxide 2 : 

/OCH3 

CO( + HOH -> CH3OH + HC1 + C0 2 
N C1 

Methyl chloroformate does not liberate iodine from sodium 
iodide, nor bromine from lithium bromide. 3 

By the action of methyl chloroformate on methyl sulphuric 
acid, dimethyl sulphate is formed in good yield 4 : 

/OCH3 /OCH3 /OCH3 

CO< + S0 2 ( = S0 2 < + HC1 + C0 2 

X C1 N OH N OCH 3 

Chlorosulphonic acid also reacts with methyl chloroformate 5 
to give a good yield of methyl chlorosulphonate (see p. 266). 

Methyl chloroformate, when dissolved in methanol and treated 
with hot potassium or sodium cyanide, reacts according to the 
following equation 6 : 

/OCH3 /OCH3 
CO( + KCN = CO< + KC1 

N C1 N CN 

forming methyl cyanoformate. This is a colourless liquid with 
an ethereal odour boiling at 100° C. at ordinary pressure. S.G. 
about 1. Soluble in alcohol, ether and other organic solvents. 

1 Vles, Rec. trav. chim., 1934, 53, 964. 

2 Rose, Ann., 1880, 205, 229. 

3 A. Perret, Bull. soc. chim., 1936, 958. 

4 M. Kraft and Ljutkina, /. Obscei Khim., Ser. A., 1931, 63, 190. 

5 M. Kraft and Alexejev, /. Obscei Khim., Ser. A., 1932, 64, 726. 

6 Weddige, J.-prakt. Chem., 1874, 10, 197. 



104 HALOGEN ATED ESTERS OF ORGANIC ACIDS 

Water and alkalies decompose it, forming hydrocyanic acid, 
carbon dioxide and methyl alcohol 1 : 



This reaction forms the basis of a method for the quantitative 
determination of methyl chloroformate which consists essentially 
in treating the substance to be tested with aniline solution and 
titrating the hydrochloric acid formed. In this case it is not 
possible to determine the carbamic ester formed gravimetrically 
(as in the phosgene estimation), for it is very soluble in water. 3 

Though methyl chloroformate is a powerful lachrymator, it 
was not used alone as a war gas. 

Because of its strongly irritant properties, it has been used in 
insecticidal preparations : " Zyklon A," which is a mixture of 
90% of methyl cyanoformate and 10% of methyl chloroformate, 
and " Zyklon B," a mixture of liquid hydrocyanic acid and 
irritant chlorinated and brominated compounds. 4 

3. Mono-, di- and tri-chloromethyl Chloroformates 

These compounds were prepared by Hentschel in 1887 5 by 
the action of chlorine on methyl chloroformate. 

During the war of 1914-18 they were employed as war gases, 
especially : 

The mixture of monochloromethyl chloroformate with 
dichloromethyl chloroformate, used in 1915 by the Germans 
under the name of " K-Stoff," and later also by the Allies, 
especially the French, by whom it was called " Palite." 

Trichloromethyl chloroformate, used almost exclusively by the 
Germans, under the name of " Perstoff" (Meyer). 

The manufacture of these substances was carried out by the 
formate method or the chloroformate method, as mentioned on 
p. 99. The method of chlorination in each of these is similar 
and requires a suitable source of light. Many experiments on 
this subject have indicated that the Osram |-watt arc lamp and 
the mercury vapour lamp are suitable light sources, and the 

1 Nef, Ann., 1897, 287, 290. 

2 Wilm and Wischin, Ann., 1868, 147, 157. 

3 Vles, Rec. trav. chim., 1934, 53, 964. 

* Frickhinger, Gase in der Schadlingsbekampfung, Berlin, 1933, 27. 
s Hentschel, /. prakt. Chem., 1887, 36, 99. 




'CN 



With aniline, methyl chloroformate reacts as follows : 




+ HCl 



THE CHLOROMETHYL CHLOROFORM ATES 105 



latter is to be preferred owing to its light being rich in ultraviolet 
radiation. 1 

By this means a mixture of the three chloro-derivatives is 
generally obtained, and these may be separated by fractional 
distillation : 

Monochloro-derivative . b.p. 106-5° to 107° C. 
Dichloro-derivative . . b.p. 110° to 111° C. 
Trichloro-derivative . . b.p. 127-5° to 128° C. 

Separation of the mono- and dichloro-derivatives is difficult 
because of the closeness of their boiling points, but the trichloro- 
compound is very easily separated from the mono- and dichloro- 
compounds. 

Laboratory Preparation 

Various Chloro-derivatives* 100 gm. methyl formate are 
placed in a 250 ml. flask fitted with a reflux condenser and a 
glass inlet tube for chlorine, and the whole weighed. The 
contents of the flask are heated to boiling and then a current 
of chlorine introduced, exposing the reacting substances to 
direct sunlight as far as possible, or to the light from a 500-watt 
lamp. By properly regulating the temperature and the addition 
of the chlorine and occasionally weighing the flask and its contents 
it is possible to obtain any of the chloro-derivatives. The 
reaction-product is fractionally distilled under reduced pressure. 

Trichloromethyl Chloroformate. 3 100 ml. of methyl formate are 
placed in a flask connected by a ground-glass joint with a 
condenser containing ice and salt. From the commencement 
the flask is exposed to a 500-watt lamp, and the current of 
chlorine then started and maintained at a very low speed in the 
early phase, so that the temperature is maintained at 30° C. 
As the reaction proceeds the rate of addition of the chlorine is 
gradually increased, so that the temperature finally reaches 
about 90° C. The chlorination is complete after about 30 hours. 

The product obtained is distilled under reduced pressure in an 
all-glass apparatus provided with a fractionating column and a 
condenser. The middle fraction, boiling between 50-0° and 
50-4° C. at 48 mm., is collected in a receiver containing calcium 
chloride. In order to purify the product it is redistilled. Yield 
about 70% of theoretical. 4 

1 Grignard, Compt. rend., 1919, 169, 1074 ; A. Kling and coll., Compt. rend., 
1919, 169, 1046. 

» Hentschel, /. prakt. Chem., 1887, 36, 213-305; Florentin, Bull. soc. 
chim., 1920, 27, 97 ; Barthelemy, Rev. prod, chim., 1922, 25, 685. 
3 Ramsperger and Waddington, /. Am. Chem. Soc, 1933, 55, 214. 
* Stolzenberg, op. cit. 



io6 HALOGEN ATED ESTERS OF ORGANIC ACIDS 



Industrial Manufacture 

During the war of 1914-18 both of the methods described were 
used — the formate method and the chloroformate method. 

The Formate Method. This method was used in the Bayer 
plants in Germany. It was very costly, chiefly because 

concentrated formic acid was 
needed for the preparation of 
the formate. 

The methyl formate was 
obtained as described on 
page 101, and was chlori- 
nated in special vessels A 
(Fig. 6), 2-3 m. in diameter 
and 1-5 m. in height, fitted 
with an agitator B. These 
vessels were of cast iron, lined 
with lead, or often enamelled. 
The gaseous chlorine was led 
in at the bottom of the vessel through the pipe C and the 
reaction accelerated by employing eight Osram lamps (L) of 
4,000 candle-power, placed in the upper part of the vessel. 
The heating of the reaction-mass is carried out by means of 
steam coils or by the electrical resistances, S. 

In order to obtain the less highly chlorinated products the 
reaction is suitably regulated and lamps of a lower intensity 
employed. By chlorinating more vigorously, however, and using 
a mercury-vapour lamp it is very easy to obtain the trichloro- 
compound. 

After the chlorination the product is distilled in special vessels 




Fig. 6. 




Fig. 



lined with porcelain (Fig. 7) heated by the coils B. The fraction 
boiling at lower temperatures is condensed in S t (cooled by 



MONOCHLOROMETHYL CHLOROFORM ATE 107 



water) and S 2 (cooled by ice), and then collected in the receiver R. 
The more highly chlorinated product remains in A. 

The Chloroformate Method. This method is less expensive and 
more suited to large-scale manufacture than the preceding. It 
was used in Germany by the Hoechst works and later also in 
France. 

The chlorination of the chloroformate, obtained by the method 
given on p. 102, was carried out like that of methyl formate, in 
lead-lined or enamelled vessels. The lids of these vessels were 
also enamelled and carried eight Osram lamps protected by glass 
bells. The chlorine was introduced through eight pipes. 

According to Grignard, the chlorination must commence in 
the gaseous phase, and so the methyl chloroformate is first 
heated in such a way as to produce a slight pressure, then the 
lamps switched on and the chlorine then introduced at such a 
rate as to prevent the reaction from being violent. The product 
may be rectified as described in the preceding method. 

Physical and Chemical Properties 

The chloro-derivatives of methyl chloroformate are all 
colourless liquids at ordinary temperatures, have boiling points 
close together and dissolve easily in organic solvents. All are 
hydrolysed by water even at ordinary temperatures and react 
readily with various compounds. 

(a) MONOCHLOROMETHYL CHLOROFORMATE (M.Wt. 128-9) 

ClCOOCH 2 Cl. 

This is a mobile, colourless liquid with an irritating odour, 
which boils at 106-5° to 107° C. at ordinary pressure and at 
52-5° to 53° C. at 100 mm. of mercury. It has a S.G. of 1-465 at 
15° C, while its vapour density is 4-5 (air = 1). The vapour 
tension at io° C. is 3-6 mm. and at 20° C. 5-6 mm. 

Monochloromethyl chloroformate is hydrolysed by water at 
ordinary temperatures ; this decomposition takes place more 
rapidly and completely by the action of hot water or in the 
presence of alkali. Formaldehyde, hydrochloric acid and carbon 
dioxide are formed : 

/OCH 2 Cl 

CO< + H 2 0 = HCHO + 2 HC1 + C0 2 

This behaviour of the monochloro-derivative is applied in the 
identification and quantitative determination in air of the 
industrial product (see pp. 123, 124). 



io8 HALOGEN ATED ESTERS OF ORGANIC ACIDS 



Monochloromethyl chloroformate, like phosgene, liberates 
iodine from sodium iodide, but the reaction is not quantitative, 
proceeding only to about 70% completion. 1 

/OCHXl 

C0 \ CI ' + 2 Nal = CH 2 0 + I 2 + CO + 2 NaCl 

Like methyl chloroformate, but unlike the di- and tri-chloro- 
derivatives, it does not liberate bromine from lithium bromide. 

Ferric chloride and anhydrous aluminium chloride decompose 
chloromethyl chloroformate even in the cold, while on heating 
to about 70° C. the reaction is more rapid, 2 phosgene being 
formed. 

/OCH 2 Cl 
CO< COCl 2 + CH 2 0 

N C1 

Alcohols react energetically, giving hydrochloric acid and the 
corresponding monochloromethyl carbonate : 

/OCHXl /OCH 2 Cl 
CO< + R-OH = CO< + HC1 

N C1 N OR 

With sodium phenate, reaction takes place at the ordinary 
temperature with formation of sodium chloride and phenyl 
monochloromethyl carbonate : 

/OCH 2 Cl /OCH 2 Cl 
CO< + C 6 H 6 -ONa = CO< + NaCl 

N C1 N OC 6 H 5 

Monochloromethyl chloroformate, unlike methyl chloroformate, 
reacts with difficulty with chlorosulphonic acid, forming 
monochloromethyl chlorosulphonate only after boiling on the 
water bath for 4 hours 3 : 



CO( + S0 2 ( = S0 2 < + HC1 + CO. 

N C1 X C1 X C1 



This is a colourless liquid, boiling at 49 0 to 50 0 C. at a pressure 
of 14 mm. of mercury ; its S.G. is 1-63 at room temperature. It 
has powerful irritant properties. 4 

By the action of methyl sulphuric acid on monochloromethyl 

1 A. Perret, Bull. soc. chim., 1936, 957. 

* A. Kling and D. Florentin, Compt. rend., 1919, 169, 1166. 

3 M. Kraft and Alexejev, /. Obscei Khim., Ser. A., 1932, 64, 726. 

* Fuchs and Katscher, Ber., 1927, 60, 2292. 



DICHLOROMETHYL CHLOROFORM ATE 109 

chloroformate, methyl chlorosulphonate is formed (see p. 266), 
according to the following (Kraft) : 

/OCH 2 Cl /OCH3 /OCH3 

CO< + S0 2 ( = S0 2 ( + HC1 + C0 2 + CH 2 0 

N C1 N OH X C1 

Monochloromethyl chloroformate also reacts with benzoic acid, 
forming monochloromethyl benzoate (Kraft) : 

/OCH 2 Cl 

CO( c) + C 6 H 5 COOH = C 6 H 6 COOCH 2 Cl + HC1 + C0 2 

The toxicity of monochloromethyl monochloroformate is 
relatively slight. Its lachrymatory power is, however, con- 
siderable ; the minimum concentration capable of producing 
lachrymation is 2 mgm. per cu. m. of air. The limit of 
insupportability is 50 mgm. per cu. m. of air (Flury). 1 

(b) DICHLOROMETHYL CHLOROFORMATE (M.Wt. 163*4) 

Cl.CO.OCHCl 2 . 

Colourless liquid, boiling at no 0 to iii° C. at 760 mm., and at 
54° to 55° C. at a pressure of 100 mm. of mercury. Its S.G. is 
1*56 at 15° C, and its vapour density is 5-7 (air = 1). 

The vapour tension varies with the temperature as shown in 
the following table : 

TEMPERATURE VAPOUR TENSION 

° C. MM. MERCURY 

10 3-6 
20 5 
30 6 

This compound in contact with water decomposes as follows : 

CI— COOCHCl 2 + H 2 0 = CO + C0 2 + 3HCI. 

The hydrolysis proceeds fairly rapidly, even in the cold, but 
is much accelerated by heating and even more so by addition 
of alkali. 

Dichloromethyl chloroformate reacts with cold potassium 
iodide, liberating iodine : 



co(' 

Y 



OCHCl 2 

+ 3 KI = 3 KC1 + HI + 2 CO + I 2 

CI 



In this reaction carbon monoxide is evolved quantitatively. 2 

1 Flury, Z. ges. exp. Med., 1921, 13, 567. 

8 A. Perret and J. Biechler, Compt. rend., 1936, 86. 



no HALOGEN ATED ESTERS OF ORGANIC ACIDS 

The dichloro-compound reacts with lithium bromide (unlike 
the monochloro-derivative) 1 : 

/OCHCl 2 

CO( + 2 LiBr = 2 CO + 2 LiCl + HC1 + Br, 

X C1 

Ferric chloride and anhydrous aluminium chloride decompose 
dichloromethyl chloroformate slowly at ordinary temperatures 
and rapidly at 8o° C, forming a mixture of carbon dioxide and 
chloroform 2 : 

CI — COOCHCl 2 = C0 2 + CHC1 3 . 

Like the preceding compound, it reacts with alcohols, forming 
hydrochloric acid and the corresponding dichloromethyl 
carbonate : 

/OCHCL /OCHCl 2 
CO< + R-OH = CO< + HC1 

N C1 N OR 

and with sodium phenate forming sodium chloride and phenyl 
dichloromethyl carbonate : 

/OCHCl 2 /OCHC1, 
CO( + C 6 H 5 ONa = NaCl + CO( 

Vl X OC 6 H 5 

Aniline in aqueous or benzene solution reacts with 
dichloromethyl chloroformate to give diphenylurea and 
formanilide according to the equation : 

,OCHCl 2 /NHC 6 H 5 ,NHC 6 H 5 

CO( +3 C 6 H 5 -NH 2 = CO( + CO< +3 HC1 

N C1 NHC 8 H 5 X H 

Dichloromethyl chloroformate is less irritant than the preceding 
compound, but more toxic. Its limit of insupportability is 
75 cu. mm. per cu. m. (Flury). 

(c) Trichloromethyl Chloroformate (M.Wt. 197-85) 

CI.CO.OCCI3. 

Colourless mobile liquid with an irritating odour slightly 
reminiscent of phosgene. It is also known as " Diphosgene." 

At ordinary pressure it boils at 127-5° to 128° C. and at a 
pressure of 18 mm. at 41° C. It solidifies at — 57° C. Its S.G. 
is 1-65 at 15° C. and its vapour density 6-9 (air = 1). Its refractive 
index at 22° C. is 1-45664. 

1 A. Perret, Bull. soc. chim., 1936, 350. 

a A. Kling and D. Florentin, loc. cit. ; Grignard, Rivat, etc., Compt. rend., 
1919, 169, 1074, 1 143. 



TRICHLOROMETHYL CHLOROFORM ATE in 



The variation of vapour tension with temperature is as follows 
(Herbst) : 

TEMPERATURE VAPOUR TENSION 

° C. MM. MERCURY 

o 3 
io 5 

20 IO'3 

30 16-3 

It dissolves in benzene and in many other organic solvents. 
At the ordinary temperature it dissolves in 24 parts by weight 
of phosgene. 

On heating this compound it decomposes, forming phosgene 
according to the equation 1 : 

/OCCI3 /CI 
C0< -> 2 C0< 

N C1 N C1 

This decomposition takes place also at ordinary temperatures 
when trichloromethyl chloroformate comes into contact with 
substances having a porous structure such as activated carbon, 
or with iron oxide, 2 etc. 

Trichloromethyl chloroformate reacts with cold water very 
slowly, but hot water or alkalies accelerate this, hydrochloric 
acid and carbon dioxide being formed : 

CI— COOCCI3 + 2H 2 0 = 2C0 2 + 4HCI. 

By heating to boiling with alkali carbonates it decomposes to 
form sodium chloride and carbon dioxide : 

CI— COOCCI3 + 2Na a C0 3 = 4NaCl + 4C0 2 . 

With sodium iodide in acetone solution it reacts rapidly and 
quantitatively as follows : 

/°cci 3 

C0< + 4 Nal = 2 I 2 + 4 NaCl + 2 CO 
N C1 

The reaction with lithium bromide is similar. 3 
Ammonia reacts vigorously, forming urea and ammonium 
chloride : 

/OCCI3 /NH 2 
C0< 4- 8 NH 3 = 4 NH 4 C1 + 2 C0( 
N C1 NH 2 

1 Cahours, Ann. Mm. phys., 1847, 352 ; Hentschel, /. prakt. Chem., 1887, 
36, 99, 209 ; Ramsperger, /. Am. Chem. Soc, 1933, 55, 214. 

2 H. P. Hood and H. Murdoch, /. Phys. Chem., 1919, 23, 498. 
8 A. Perret, Bull. soc. chim., 1936, 350. 



ii2 HALOGEN ATED ESTERS OF ORGANIC ACIDS 



With hexamethylene tetramine it reacts, like phosgene, to 
form an addition product of the formula 1 : 

C0C1 2 .2(CH 8 ) 6 N 4 . 

Ferric chloride and anhydrous aluminium chloride decompose 
trichloromethyl chloroformate into carbon tetrachloride and 
carbon dioxide 2 : 

/OCCI3 
C0( CC1 4 + CO, 

X C1 

Trichloromethyl chloroformate does not react with concentrated 
hydrochloric acid. 

With alcohols it reacts similarly to the other members of this 
group to form the corresponding trichloromethyl carbonate : 

/OCCI3 /OCCI3 
CO( + R-OH = CO< + HC1 

X C1 Ndr 

However, if the alcohol is in excess and the reaction proceeds 
in the cold, its course is different 3 : 

/OCClj, /OR 
CO< + 3 ROH = 2 CO( + 3 HC1 
N OR N OR 
The nature of the alcohol also affects the nature of the products 
formed. Thus with most primary alcohols the reaction described 
above takes place, but if there are present in the molecule of 
the primary alcohol radicles of high molecular weight, partial 
decomposition of the carbonate takes place with formation of 
phosgene and the corresponding chlorocarbonic ester, as follows 4 : 

/OCCl 3 /CI 
CO< -> COCl 2 + CO< 

Y)R N OR 
With secondary alcohols the reaction proceeds similarly, but 
with tertiary alcohols a further decomposition of the 
chlorocarbonic ester formed takes place and carbon dioxide is 
evolved and the corresponding alkyl chloride is formed : 



/ C1 
CO< 



► RC1 -f C0 2 

x OR 

With excess of aniline in aqueous or benzene solution 

trichloromethyl chloroformate reacts like phosgene, being 

1 Puschin and Mine, Ann., 1937, 532, 300. 
4 Kling and coll., loc. ext. 

1 Nekrassov and Melnikov, /. prakt. Chem., 1930, 126, 81. 

* Nekrassov and Melnikov, /. Rusk. Fis. Khim. Obsc, 1930, 62, 631, 1545. 



TRICHLOROMETHYL CHLOROFORM ATE 113 



quantitatively transformed -into symmetrical diphenylurea or 

carbanilide 1 : 

/OCCI3 /NHC 6 H 6 
C0< 4- 4 C 4 H S -NH 2 = 2 C0< +4 HC1 

N C1 " N NHCeH 5 

If, however, there is insufficient aniline, a mixture, of phenyl 
isocyanate and anilido-formyl chloride is formed : 

/OCCI3 //N-C 6 H 5 
C0< + 2 C 6 H 5 NH 2 = C< + C 6 H 5 -NH-C0C1 + 3HC1 

N C1 K) 
With dimethyl aniline in presence of aluminium trichloride or 
zinc chloride, Crystal Violet is formed. 2 

By the action of trichloromethyl chloroformate on 
diphenylamine, trichloromethyl N-diphenyl urethane results, 
together with a small quantity of tetraphenylurea 3 : 

/OCCI3 /OCCL, 
CO< + 2 (C 6 H 5 )jJJH = CO( + (CeH^^H . HC1 

This urethane forms white crystals, melting at 61 0 C, which 
on heating to 200° to 250 0 C. decompose forming phosgene and 
diphenyl carbamic chloride. Cold water decomposes it into 
diphenylamine, hydrochloric acid and carbon dioxide. 

Trichloromethyl chloroformate reacts with pyridine, forming 
a yellow crystalline substance of the formula 4 : 

C 5 H 5 N(C1)C0(C1)NC S H 5 , 
which decomposes by the action of water with evolution of 
carbon dioxide : 

C 8 H 6 N(C1)C0(C1)NC 5 H 6 + H 2 0 = 2(C 6 H 5 N.HC1) + C0 2 . 

Like the preceding compound, trichloro methyl chloroformate 
reacts with sodium phenate, forming sodium chloride and phenyl 
trichloromethyl carbonate : 

/OCCI3 /OCCI3 
CO< -f C 6 H 5 -ONa = CO< 4- NaCl 

N C1 N OC 6 H 5 

In presence of an excess of the phenate the reaction proceeds 
further, diphenyl carbonate being formed 5 : 

/OC 6 H 3 
CO( 

X OC 6 H 5 

1 Hentschel, /. prakt. Chem., 1887, 36, 310. 

2 Hochst Farb. W., D.R.P. 34607. 

3 N. Melnikov and Vinokurov, /. Obscei Khim., Ser. A., 1932, 64, 484, 

4 D.R.P. 109933/1898. 

6 N. Melnikov, /. prakt. Chem., 193°. i 28 . 2 33- 



H4 HALOGEN ATED ESTERS OF ORGANIC ACIDS 



It also reacts with benzene to form benzophenone : 

/OCCI3 /C 6 H 5 
CO( + 4 C.H, 2 CO( +4 HC1 

N C1 X C 6 H 5 

By heating under reflux with ethylene chlorohydrin, 
dichloroethyl carbonate is formed 1 : 

/OCClo CH,OH /0CH 2 CH 2 C1 
CO< + 4 I = 2 CO< +4 HC1 

N C1 CH 2 C1 V 0CH 2 CH 2 C1 

This is a colourless liquid, boiling at ordinary pressure at 
240° C. with partial decomposition and at a pressure of 8 mm. 
at 115° C. Its specific gravity at 20 0 C. is 1-3506. It is insoluble 
in water, volatile in steam, and is slowly hydrolysed by alkalies. 

Trichloromethyl chloroformate in the pure state has no 
corrosive action on iron, and so may be loaded directly into 
projectiles of this material. 

It is completely retained by filters of activated carbon. 2 

The action of trichloromethyl chloroformate on foodstuffs 
varies according to whether these are high in water content, 
like fresh meat, milk, wine, or beer, or low in water content, like 
grain, flour, coffee, etc. The water-rich foods absorb large 
quantities of trichloromethyl chloroformate, which then 
decomposes into hydrochloric acid and carbon dioxide, so that 
their edibility depends upon the quantity of hydrochloric acid 
which they have absorbed. The drier foods can be purified, 3 
as in the case of phosgene, by exposure to a current of warm, dry 
air. 

Trichloromethyl chloroformate is less irritant than the other 
members of this group. The minimum concentration causing 
irritation is 5 mgm. per cu. m. of air (Miiller). The limit of 
insupportability is 40 mgm. per cu. m. The toxicity is about 
equal to that of phosgene, and, according to Prentiss, it is probable 
that this is not a specific property of trichloromethyl 
chloroformate, but is due to the phosgene into which it decomposes 
in contact with the tissues of the human body. 

The mortality-product is 500 according to Flury, but this 
value must be considered too low, as in the case of phosgene. 
According to American experiments on dogs, 4 the mortality- 
product of trichloromethyl chloroformate for 10 minutes' exposure 
is ten times as great — about 5,000. 

1 Nekrassov, /. prakt. Chem., 1929, 123, 160. 

2 M. Dubinin and coll., /. Prikl. Khim., 1931, 4, 1100. 

3 W. Plucker, Z. Uniersuch. Lebensmitt., 1934, 68, 317. 
* Prentiss, Chemicals in War, New York, 1937. 



HEXACHLOROMETHYL CARBONATE 115 



Statistics based on data obtained during the war of 1914-18 
show that trichloromethyl chloroformate is a war gas which when 
used in projectiles produces a large number of deaths. 



This compound, also known as " Triphosgene," was prepared for 
the first time by Councler 1 in 1880, by the chlorination of methyl 
carbonate. 

It is obtained as a by-product in the preparation of trichloro- 
methyl chloroformate when methyl chloroformate which is impure 
with dimethyl carbonate is employed. 

Laboratory Preparation 

Hexachloromethyl carbonate is prepared, according to Councler, 
by passing dry chlorine through dimethyl carbonate exposed to 
direct sunlight. After some days' chlorination colourless crystals 
separate. When the whole mass has become solid, a current of 
dry carbon dioxide is passed through to remove the chlorine and 
hydrochloric acid present. 

The product obtained is dried on filter paper, washed many 
times with a little absolute ether and dried in vacuo over sulphuric 
acid. 

Physical and Chemical Properties 

White crystals, melting at 78° to 79 0 C. It has an odour of 
phosgene and boils at ordinary pressure at 205° to 206° C. with 
partial decomposition. S.G. about 2. Soluble in benzene, carbon 
tetrachloride, ether, etc. 

On heating near its boiling point at ordinary pressures, it 
decomposes to form phosgene and diphosgene, which further 
decomposes into phosgene. The reaction of decomposition is 



The presence of catalysts such as ferric chloride facilitates this 
decomposition. 

Cold water reacts very slowly with hexachloromethyl carbonate, 



4. Hexachloromethyl Carbonate 



(M.Wt. 2967) 



CO 



/OCCL, 
x OCCl 3 



thus 2 : 




1 Councler, Ber., 1880, 13, 1698. 

s Hood and Murdoch, /. Phys. Chem., 1919, 23, 509. 



n6 HALOGEN ATED ESTERS OF ORGANIC ACIDS 

though hot water decomposes it rapidly with formation of carbon 
dioxide and hydrochloric acid : 

/OCCI3 

CO< + 3 H 2 0 = 6 HC1 + 3 C0 2 

N 0CC1 3 

Aqueous solutions of the alkali hydroxides decompose 
hexachloromethyl carbonate, forming the corresponding 
carbonates and chlorides. 

It reacts with sodium iodide and with lithium bromide in the 
same manner as trichloromethyl chloroformate, liberating iodine 
and bromine respectively. All the six chlorine atoms take part 
in this reaction, 1 which is as follows : 

/OCClo 

CO< + 6 Nal = 3 CO + 6 NaCl + 3 I 2 
N 0CC1 ? 

About 80% of the theoretical iodine is actually liberated. 2 
It reacts with aqueous aniline forming diphenyl urea 3 : 

CO(OCCl 3 ) 2 + 6C 6 H 6 NH 2 = 3CO(NHC 6 H 5 ) 2 + 6HC1. 

With sodium phenate, phenyl carbonate is formed (Grignard). 
Methanol forms trichloromethyl carbonate and methyl 
chloroformate 4 : 

/OCCI3 /OCCI3 
CO< + 2 CH 3 OH = CO< + CICOOCH3 + 2 HC1 

N OCCl 3 N OCH 3 

In presence of excess methanol, the trichloromethyl carbonate 
is converted into methyl carbonate and methyl chloroformate, so 
that the final product of the reaction with excess methanol 
present is methyl carbonate. 

It reacts with pyridine in the same manner as phosgene, 
forming a yellow crystalline substance of the formula 5 
C 5 H 5 N(C1)C0(C1)C 6 H 5 N, which decomposes by the action of water 
according to the equation : 

C 5 H 5 N(C1)C0(C1)C 5 H 5 N + H 2 0 = 2(C 6 H 5 N.HC1) + C0 2 . 

It has no corrosive action on metals. 

The physiopathological action of this compound is similar to 
that of phosgene. 

1 A. Perret and coll., Bull. soc. chim., 1936, 958. 

2 Perret, Compt. rend., 1936, 203, 84. 

3 Grignard and coll., Ann. chim., 1919, 12, 229. 

* W. Nekrassov and Melnikov, /. prakt. Chem., 1930, 126, 81. 
5 V. Heyden, D.R.P. 109933 ; Chem. Zentr., 1900 (II), 460. 



ETHYL CHLORO ACETATE 



ii7 



(B) THE ETHYL ACETATE GROUP 

The halogen derivatives of ethyl acetate are compounds which 
have been known for some time and are used nowadays for 
organic syntheses both in the laboratory and in industry. They 
have a powerful action on the eyes and were used as war gases 
in the war of 1914-18. 

They are commonly prepared by the esterification of ethyl 
alcohol by the corresponding acids : monochloracetic, bromoacetic, 
etc., using sulphuric acid as dehydrating agent. This acid first 
reacts with alcohol to form ethyl hydrogen sulphate : 

C 2 H 5 OH + H a S0 4 = H 2 0 + S0 2 < 

N OH 

which then condenses with the monohalogenated acid forming 
the ester : 

S0 2 ( + CH 2 Cl-COOH = H 2 S0 4 + CH 2 C1 

OH ** 1 

COO • C 2 H 5 

The compounds of this type have the halogen atom bound very 
unstably to the remainder of the molecule. It is easily split off 
by the action of water, alkaline solutions and ammonia. This 
instability considerably reduces the value of these substances as 
war gases. 

1. Ethyl Chloroacetate (M.Wt. 122) 

CH 2 C1 

COO.C 2 H 5 . 

Ethyl chloroacetate may easily be prepared by the reaction 
of chloroacetyl chloride with alcohol, 1 or by means of the action 
of ethyl alcohol on monochloroacetic acid in presence of sulphuric 
acid : 

CH 2 C1 CH 2 C1 
I + C 2 H 5 OH =1 + H 2 0 

COOH COOCjH, 

It is also prepared by the action of phosphorus pentachloride 
on ethyl glycollate 2 : 

CH 2 OH CH 2 C1 
I + PC1 S = I + HC1 + POCI3 

COOC^ COOC 2 H 5 



1 Willm, Ann., 1857, 102, 109. 

2 A. Henry, Ann., 1870, 156, 176. 



n8 HALOGEN A TED ESTERS OF ORGANIC ACIDS 
or by the action of water on dichlorovinyl ethyl ether. 



Laboratory Preparation 1 

Into a flask of about 200 ml. capacity fitted with a reflux 
condenser, 75 gm. monochloracetic acid, 45 gm. 95% alcohol and 
10 gm. sulphuric acid (S.G. 1-84) are introduced. These are 
stirred and heated on the water-bath at 100° C. for about 5-6 hours. 
At the end of the heating the mass is allowed to cool and then 
poured into a separatory funnel containing about 150 ml. cold 
water. The ethyl chloroacetate layer is separated, washed once 
more with water and then fractionally distilled. 

Physical and Chemical Properties 

Ethyl chloroacetate is a colourless, mobile liquid with an odour 
of fruit, boiling at 143*5° C. at a pressure of 758 mm. of mercury 
(Willm) and decomposing by long heating at the boiling point. 2 
Its specific gravity is 1*1585 at 20° C, and its vapour density has 
been experimentally found to be 4-46 (Willm), while the calculated 
value is 4*23. 

It is insoluble in water, but easily soluble in the common 
organic solvents. 

It is easily decomposed by alkalies and also by hot water. 
In this decomposition, besides the saponification of the ester : 



the halogen atom of the CH 2 C1 group is also substituted by a 
hydroxyl with formation of the corresponding hydroxy-acid : 





CH,C1 



CH 2 OH 



+ HOH 




+ HCl 



COOH 



It reacts with ammonia to form chloroacetamide : 




1 Conrad, Ann., 1877, 188, 218. 

2 Vandervelde, Bull. acad. roy. belg., 1897, [3] 34, 894. 



ETHYL BROMO ACETATE 



1x9 



With potassium cyanide, ethyl cyanoacetate is formed 1 : 

CH 2 C1 CH 2 CN 
I " + KCN =| + KC1 

COOC a H 5 COOC 2 H 5 

By the action of sodium urethane on ethyl chloroacetate, N- 
chloroacetyl urethane is formed 2 : 

CH 2 C1 /NHNa CH 2 C1 

I + C0< =1 + C 2 H 6 ONa 

COOC 2 H 3 N OC 2 H 6 CONHCOOC 2 H 5 

This forms crystals melting at 129° C, sparingly soluble in cold 
water, but soluble in alcohol. 

Ethyl chloroacetate was used only to a limited extent in the 
last war. It was manufactured in large quantities, however, for 
the preparation of two other substances whose aggressive action 
was much more efficacious : ethyl bromo- and iodo-acetates. 

2. Ethyl Bromoacetate (M.Wt. 167) 

CH 2 Br 



;oo.c 2 h 5 . 

Ethyl bromoacetate, according to Meyer, 3 was the first 
substance employed in warfare as gas (at the end of 1914). At 
the beginning it was used in hand grenades, but later the French 
preferred to use it in shells. 

It was prepared for the first time by Perkin and Duppa 4 by 
treating bromoacetic acid with ethyl alcohol in a closed tube for 
1 hour in the cold : 

CH 2 Br CH 2 Br 
I + C 2 H 5 OH =| + H 2 0 

COOH COOQHs 

It may also be obtained by the action of phosphorus penta- 
bromide on ethyl glycollate 5 : 

CH 2 OH CH 2 Br 
I + PBr 5 =| + HBr + POBr 3 

COOC,!^ COOQHs 

1 Mueller, Ann., 1865, 131, 351. 
8 Diels, Ber., 1903, 36, 745. 
» Meyer, op. cit. 

* Perkin and Duppa, Ann., 1858, 108, 106. 
5 Henry, Ann., 1870, 156, 174. 



120 HALOGEN ATED ESTERS OF ORGANIC ACIDS 



or by the action of bromine on sodium ethylate 1 : 

2 QsHgONa + 2 Br, = C^Br + CH 3 • COOH + 2 NaBr + HBr 

CaH 6 ONa + CH 3 COOH + HBr = CH 3 • COOC^ + NaBr +H 2 0 

CH S CHjBr 
I + Br 2 = | + HBr 

COOCjHs COOQHs 

It is generally prepared by the action of bromine on acetic 
acid in presence of red phosphorus. 2 Phosphorus pentabromide 
is formed first, and this reacts with the acetic acid, forming acetyl 
bromide, as follows : 

CH3COOH + PBr 5 = POBr 3 + HBr + CH 3 — COBr 
This reacts with more bromine, forming bromoacetyl bromide 

CH 3 COBr + Br 2 = HBr + CH 2 Br— COBr, 
which with alcohol forms the ester : 

CH 2 Br— COBr + C 2 H 5 OH = HBr + CH 2 Br — COOC 2 H 6 . 

Laboratory Preparation 3 

30 gm. glacial acetic acid with 3-9 gm. red phosphorus are 
placed in a flask fitted with a stopper containing two holes. 
Through one of the holes passes a tap-funnel ; through the other 
a condenser which is joined at its upper end, by means of a glass 
tube, to a small flask containing water, in such a manner that the 
tube does not dip into the water. While stirring vigorously and 
cooling with water, 50 gm. bromine are slowly added from the 
tap-funnel and the flask warmed on the water-bath to 6o° to 65° C. 
while a further 85 gm. bromine are added a little at a time. 
When all the bromine has been added, the flask is heated on a 
boiling water-bath until no more hydrobromic acid is evolved. 
The flask is then cooled to about 0° C, and 35 gm. absolute 
alcohol added from the tap-funnel in small portions with constant 
stirring. 6 gm. sulphuric acid are also added and the flask 
stirred and heated on the boiling water-bath for about 2 hours. 
At the end of this time the flask is again cooled and the reaction- 
product poured into water. The oily layer is separated, washed 
with water, dried over calcium chloride and distilled, collecting 
the fraction boiling between 155° and 175 0 C. The yield is about 
80% of theoretical. 

1 Sell and Salzmann, Ber., 1874, 7, 496. 

2 Selinski, Ber., 1887, 20, 2026. 

3 Auwers and Bernhardi, Ber., 1891, 24, 2216 ; Naumann, Ann., 1864, 
129, 268. 



ETHYL IODO ACETATE 



121 



Physical and Chemical Properties 

Ethyl bromoacetate is a clear, colourless liquid boiling at 
ordinary pressure at 168 0 C. 1 On cooling by means of a mixture 
of carbon dioxide and ether, it solidifies in colourless needles 
which melt at — 13-8° C. Its specific gravity is 1-53 at 4 0 C. In 
the vapour state it has a density of 5-8. It is insoluble in water 
but soluble in most of the organic solvents. Its volatility at 
20° C. is 21,000 mgm. per cu. m. of air. 

Chemically it is not a very stable compound, and is partially 
decomposed even by water and completely by sodium or potassium 
hydroxide solutions on boiling. The hydrolysis is as follows : 

CILjBr— COOC a H 5 + 2 NaOH=CH 2 OH— COONa+C 2 H 6 OH+NaBr. 

Ethyl bromoacetate on treatment with mercury ethyl at 
150° C. decomposes according to the equation 2 : 

CH 2 Br— COOC 2 H 5 +Hg(C 2 H s ) 2 = C 2 H 6 HgBr +CH 3 — COOC 2 H s + C 2 H 4 . 

Ethyl bromoacetate, because of its relatively high boiling point 
and its low volatility can be used in shells without causing a 
visible cloud on bursting. 

It has no corrosive action on iron. 

The limit of insupportability for man is 40 mgm. per cu. m. of 
air (Flury). The minimum concentration capable of provoking 
irritation of the eyes is 10 mgm. per cu. m. The product of 
mortality is 3,000 (Miiller). 

3. Ethyl Iodoacetate (M.Wt. 214) 

CH 2 I 

COO.C 2 H 5 . 

Ethyl iodoacetate was used by the Allies in shells, especially 
in mixtures with chloropicrin (10%). 

This substance cannot be prepared, like the two preceding, by 
esterification of iodoacetic acid with ethyl alcohol. It is necessary 
to start with ethyl chloroacetate or bromoacetate, both of which 
react with potassium iodide to form the iodo-compound. 

Perkin and Duppa, 3 commencing with ethyl bromoacetate and 
potassium iodide, prepared ethyl iodoacetate for the first time. 

Laboratory Preparation 

25 gm. ethyl chloroacetate are dissolved in 150 ml. alcohol in a 
flask fitted with a reflux condenser, then 35 gm. potassium iodide 

1 Perkin, /. Chem. Soc, 1894, 65, 427. 

2 Sell and Lipmann, Z. f. Chem., 1886, 724. 

3 Perkin and Duppa, Ann., 1859, 112, 125. 



122 HALOGEN ATED ESTERS OF ORGANIC ACIDS 



are added and 25 ml. water. The mixture is heated on a water- 
bath at 40° to 50° C, stirring frequently. After heating for 
1-2 hours, the mixture is transferred to a separatory funnel 
containing about 200 ml. water. The oily layer is separated, 
dried over calcium chloride and distilled. 

The ethyl iodoacetate should be stored in a dark place in order 
to prevent decomposition. 

Physical and Chemical Properties 

Ethyl iodoacetate is a colourless, dense liquid boiling at 
ordinary pressure at 179 0 C. and at a pressure of 16 mm. at 
76° to 78 0 C. 1 Its specific gravity is i-8. 

The vapour tension varies with temperature as follows : 

0 C. MM. MERCURY 

IO 0-28 

20 0-54 
30 0-87 

The vapour density is 7-4 and the volatility at 20 0 C. is 3,100 
mgm. per cu. m. (Miiller). Like most organic compounds 
containing iodine, it decomposes easily in the air and light, 
becoming brown by separation of iodine. 

It is very slowly decomposed by water and alkaline solutions 
in the cold 2 but more rapidly on warming. 3 The reaction is as 
follows : 

CH 2 I— COOC 2 H 6 +2NaOH=NaI+CH 2 OH.COONa+C 2 H 5 OH. 

Ethyl iodoacetate also reacts easily with sodium thiosulphate. 
The velocity of this reaction has been studied by Slator. 4 

It is completely decomposed by heating with nitric acid. 5 

Owing to their low volatility these esters are rarely employed 
in warfare in the pure state. They are generally diluted with 
either alcohol or ethyl acetate. 

It is particularly as an eye irritant that ethyl iodoacetate 
functions, and it seems that this is due to iodoacetic acid and not 
hydriodic acid. 

The minimum concentration capable of producing irritation of 
the eyes is 1-4 mgm. per cu. m. of air, according to Fries. The 
limit of insupportability is 15 mgm. per cu. m. and the product 
of mortality is 1,500 (Miiller). 

1 Tiemann, Ber., 1898, 31, 825. 

a Rona, Z. ges. exp. Med., 1921, 13, 16. 

3 Butlerov, Ber., 1872, 5, 479. 

4 Slator, /. Chem. Soc, 1905, 87, 482. 
6 Nef, Ann., 1897, 298, 353. 



HALOGEN ATED ESTERS: IDENTIFICATION 123 



Analysis of the Halogenated Esters 

Identification 

The various chlorinated methyl chloroformates are identified 
by the diverse manners in which they react with alkali. The 
method described dates from Hentschel in 1887 and is still used 
to-day. 1 

Identification of Monochloromethyl Chloroformate. Monochloro- 
methyl chloroformate when treated with water or aqueous sodium 
hydroxide is decomposed even in the cold according to the 
equation : 

CI— COOCH 2 Cl + H 2 0 = CH 2 0 + C0 2 + 2HCI, 

producing formaldehyde which may be easily identified by one 
of the common reagents for an aldehyde, such as the Schiff 
reagent, a 0-025% aqueous solution of fuchsin decolorised with 
sulphur dioxide. 

As the other chlorinated methyl chloroformates when they 
react with alkaline solutions form no formaldehyde, this method 
may be used for the identification of the monochloro derivative 
even in the presence of di- and tri- methyl chloroformates. 

Identification of Dichloromethyl Chloroformate, On treating 
dichloromethyl chloroformate with water or an alkaline solution 
it decomposes according to the following equation : 

CI— COOCHC1, + H 2 0 = CO + C0 2 + 3HCI, 

thus forming carbon monoxide, unlike the other derivatives. By 
applying one of the usual methods for the identification of this 
carbon monoxide, evolved when the substance being examined 
is treated with an alkaline solution, the presence of dichloromethyl 
chloroformate may be confirmed. 

Identification of Trichloromethyl Chloroformate. This substance 
may be identified by its reaction with an aqueous solution of 
aniline (3 : 100). Like phosgene and dichloromethyl chloro- 
formate, a white crystalline precipitate of diphenyl urea forms, 
which may be confirmed by microscopic examination (rhombic 
prisms) or by a determination of its melting point (236° C.). 

Identification of trichloromethyl chloroformate may also be 
made by using dimethyl amino benzaldehyde and diphenylamine 
paper, prepared as described on p. 81. In presence of trichloro- 
methyl chloroformate this turns yellow as in the presence of 
phosgene. 

1 Hentschel, /. prakt. Chem., 1887, 36, 99, 305. 



124 HALOGEN ATED ESTERS OF ORGANIC ACIDS 



Quantitative Determination 

The quantitative determination of the chloromethyl chloro- 
formates is carried out by making use of the same reactions as 
those described above for their identification. 1 

Determination of Monochloromethyl Chloroformate. The 
substance under examination is treated with sodium hydroxide 
and the amount of formaldehyde formed is then determined. 

In practice, about 0-4 ml. of the substance is accurately 
weighed into a graduated 125 ml. flask containing 50 ml. normal 
sodium hydroxide solution. After stoppering, this is then shaken, 
then allowed to stand for \ hour and made up to volume. 25 ml. 
of the alkaline liquid obtained are placed in a burette and allowed 
to drop into an excess of a decinormal iodine solution, shaken and 
allowed to stand for about 20 minutes. The following reaction 
then takes place : 

CH 2 0 + I 2 + 3NaOH = HCOONa + 2NaI + 2H 2 0. 

The solution is slightly acidified with dilute sulphuric acid and 
the excess of iodine titrated with thiosulphate. A blank should 
be carried out. 2 

Then the quantity of formaldehyde is given by the following, 
as a percentage : 

N x 0-0015 x 5 x 100 0 75 JV 
CH 8 0% = = 

in which N is the number of ml. of iodine used and P the 
weight of substance taken. From this value the content of 
CI — COOCH 2 Cl in the sample may be calculated from the 
knowledge that 1 gramme-molecule of formaldehyde corresponds 
to one of monochloromethyl chloroformate : 

CI — COOCH 2 Cl + H 2 0 = CH 2 0 + C0 2 + 2HCI. 

Determination of Dichloromethyl Chloroformate. The sample to 
be examined is treated with sodium hydroxide and the volume of 
carbon monoxide evolved is measured. 

0'3~°'5 6 111 ' 01 the substance is introduced into a Lunge 
nitrometer over mercury and 10 ml. of a 4 N solution of sodium 
or potassium hydroxide added. The carbon monoxide which is 
formed is collected and its volume measured. From the knowledge 
that 1 gramme-molecule of carbon monoxide is obtained from 

1 M. Delepine, Bull. soc. chim., 1920, [4] 27, 39. 

a Method suggested by Romijin, Z. anal. Chem., 1897, 36, 18. 



HALOGEN ATED ESTERS : DETERMINATION 125 



1 gramme-molecule of dichloromethyl chloroformate, the amount 
of the latter present in the sample may be calculated : 

CI— COOCHCLj + H 2 0 = C0 2 + CO + 3HCI. 

Determination of Trichloromethyl Chloroformate. The quantita- 
tive determination of trichloromethyl chloroformate may be 
carried out by the aniline method according to Pancenko. 1 
unless mono- or dichloromethyl chloroformate is present. These 
both react with aniline in the same way as the trichloro derivative 
(see p. 110). 

0'3-0'4 gm. of the substance to be examined is weighed into a 
small glass bulb which is then sealed and placed in a cylinder 
containing an aqueous solution of aniline as in the determination 
of phosgene. The bulb is broken and shaken in the cylinder for a 
few minutes, allowed to stand and then the diphenylurea 
determined as in the method described on p. 83. 

Quantitative Determination of Monochloromethyl Formate in 
presence of Monochloromethyl Chloroformate. In controlling the 
manufacture by analysis it is frequently necessary to determine 
the quantity of chloroformate present in the chlorination product 
of methyl formate ; that is, to determine if the product obtained 
from the methyl formate still contains some hydrogen in the 
form of HCO — group which is not substituted by chlorine. 

The method proposed by Delepine 2 for carrying out this 
determination depends on the differences between the behaviour 
of the chloromethyl chloroformates when treated with alkaline 
solutions. As already described, monochloromethyl chloro- 
formate on treatment with alkali gives formaldehyde, carbon 
dioxide and hydrochloric acid according to the equation : 

CI— COOCH 2 Cl + H 2 0 = CH 2 0 4- 2HCI + C0 2 , 

while the chlorinated methyl formates hydrolyse to form formic 
acid, formaldehyde and hydrochloric acid : 

H — COOCH 2 Cl + H 2 0 = HCOOH + CH 2 0 + HCl, 

so that the amount of formic acid found after hydrolysing a 
sample is proportional to the chloromethyl formate present. 
The determination of the formic acid may be made by titration 
with potassium permanganate 3 : 

2 KMn0 4 + 3HCOOK + KOH = 3K 2 C0 3 + 2MnO(OH) 2 . 

1 Pancenkso, Methodi Issliedovanija i chimiceskie Svoista Otravljajuscix 
Vescectv, Moscow, 1934, io 5- 

2 Delepine, loc. cit. 

» Smith, Analyst, 1896, 21, 148. 



126 HALOGEN ATED ESTERS OF ORGANIC ACIDS 



However, as the formaldehyde formed by the hydrolysis of 
monochloromethyl chloroformate is also oxidised by potassium 
permanganate it must be first determined by titration with 
iodine solution. Then, by subtracting from the number of ml. 
permanganate solution decolorised, twice the number of ml. of 
iodine solution used (for formaldehyde needs twice as much 
oxygen as formic acid for its oxidation), the result is the number 
of ml. permanganate corresponding to the quantity of formic acid 
present and from this the chloromethyl formate in the sample may 
be calculated. 



CHAPTER IX 



AROMATIC ESTERS 

On halogenating the homologues of benzene, two series of 
compounds with very different physical and chemical, but 
especially physiopathological, properties may be formed, 
according to whether the halogen atom enters the side chain or 
the benzene nucleus. While the compounds with a halogen atom 
in the side chain, like benzyl chloride (I), are efficient lachrymators, 
those with a halogen atom in the nucleus, like o-chlorotoluene (II), 
have no lachrymatory action at all. 

CH 2 C1 CH 3 

/\ /\ci 



I II 

In preparing the war gases of this group it is therefore necessary 
to employ methods which will ensure the halogen entering the 
side chain rather than the nucleus. In general it is advisable to 
carry out the halogenation at the boiling point of the hydrocarbon 
or under the influence of a light-source rich in ultra-violet 
radiations, such as diffused sunlight, the mercury-vapour lamp, 
etc. Attempts to use catalysts have not been successful, for 
catalysts, though accelerating the halogenation, orient the 
halogen into the nucleus, even when the operation is carried out 
at the boiling point of the hydrocarbon. 

Examination of the physiopathological properties of these 
halogen compounds has shown that the lachrymatory power is 
increased by an increase in the atomic weight of the halogen 
present, that is, the iodo-compounds are biologically more 
efficient than the bromo-compounds and these more efficient 
than the chloro-compounds. 

In the war of 1914-18 these substances had a limited use. 
On the one hand, the raw material for their preparation (toluol) 
was too costly, and on the other their lachrymatory power was 
soon surpassed by that of other substances. 

137 



128 



AROMATIC ESTERS 



Research carried out in the latter part of the war and continued 
in the post-war period has shown that the introduction of certain 
radicles into the molecules of these substances considerably 
increases their aggressive power. The entry of the N0 2 -group 
into the benzene nucleus in the ortho-position to the side chain 
containing the halogen, and the introduction of the CN-group 
into the halogenated side chain itself are particularly efficacious. 

Thus among the halogen-compounds containing the N0 2 -group, 
-fl-nitrobenzyl chloride (I) and bromide (II) are superior to the 
corresponding simple halogenated derivatives. 



CH 2 C1 

/\no. 



CH 2 Br 

/\no 2 



I 



II 



These may be easily obtained by halogenation of nitrotoluene or 
nitration of the corresponding halogenated toluene. 1 Moreover, 
it appears that the introduction of the N0 2 -group confers vesicant 
power on these substances. 2 

A study of those compounds in which the CN-group is in the 
side chain containing the halogen atom has indicated that 
chlorobenzyl cyanide, 3 and bromobenzyl cyanide to an even 
greater degree, have an increased lachrymatory power. These 
compounds are described in the chapter on " Cyanogen 
Compounds " (see p. 196). 

Later benzyl fluoride was prepared by the decomposition of 
benzyl trimethylammonium fluoride 4 : 

C 6 H 8 CH 2 N(CH 3 )3F^N(CH 3 ) 3 + C 6 H 6 CH 2 F. 

This is a colourless liquid boiling at 139-8° C. at a pressure of 
753 mm. and at 40° to 40-5° C. at 14 mm. pressure. Density, 
1-022 at 25° C. On cooling strongly, it solidifies to acicular 
crystals, melting at — 35° C. It does not fume in air and has no 
lachrymatory properties. Treatment with nitric acid converts 
it into nitrobenzyl fluoride. The ^-compound was isolated as 
acicular crystals melting at 38-5° C. 

1 Moureu, Bull. soc. chim., 192 1, 29, 1006. 

2 Nekrassov, he. cit. 

s Michael, Ber., 1892, 25, 1679 ; Chrzaszczevska and Popiel. Roczniki Chem., 
1927. 7, 74. 
4 C. Ingold, /. Chem. Soc, 1928, 2249. 



BENZYL CHLORIDE : PREPARATION 129 



1. Benzyl Chloride. C 6 H 5 — CH 2 C1. (M.Wt. 126-51) 

Benzyl chloride was prepared in 1853 by Cannizzaro 1 by 
acting on benzyl alcohol with hydrochloric acid. It is 
particularly well known for its use in organic synthesis. It was 
used as a war gas in the war of 1914-18, but only for a short 
time. To-day its importance is as a raw material for the 
preparation of bromobenzyl cyanide. 

Laboratory Preparation 

Benzyl chloride may be prepared in the laboratory by the 
action of chlorine on benzyl alcohol. 

100 gm. toluene and 5 gm. phosphorus pentachloride are placed 
in a flask of about 250 ml. capacity, and the whole is then weighed. 
A reflux condenser is connected to the flask, whose contents are 
then warmed to gentle ebullition, and at the same time a rapid 
current of dry chlorine is passed in. This is continued until the 
contents of the flask have increased by about 35 gm., that is, 
until 1 gramme-atom of chlorine has been absorbed. The 
chlorine absorption is accelerated by the action of sunlight. 

The reaction product is then fractionally distilled. Unchanged 
toluene first passes over, and then, between 160 0 and 190 0 C, the 
benzyl chloride, which is purified by further fractionation. 

Industrial Manufacture 

On the industrial scale also benzyl chloride is prepared by 
the action of chlorine on toluene. The toluene is first placed in a 
large cast-iron vessel A (Fig. 8), which is lead-lined and fitted 



















in 


si £ 

T\ M° 






1 


H \ 












— | 


f °L 

1 


1 MM 


l: 


J 



Fig. 8. 



WAR GASES. 



1 Cannizzaro, Ann., 1853, 88, 130. 



5 



13° 



AROMATIC ESTERS 



with a lid, and then a current of chlorine is introduced from a 
cylinder mounted on a weighing machine, so that the weight of 
chlorine used may be controlled. The mixture is then heated 
with steam generated in the boiler C ; it may be illuminated by 
means of the apparatus D. Above the reaction vessel a reflux 
condenser E is arranged, and this is connected to the receivers F 
and F 1 , in which the evolved hydrochloric acid is collected. As 
the chlorination proceeds the product passes from the vessel A 
into the receiver G, and thence into the apparatus H, where it is 
distilled. The distillate containing the benzyl chloride is collected 
in the special receivers M, N. 

Physical and Chemical Properties 

Benzyl chloride is a colourless liquid which boils at ordinary 
pressure at 179° C. 1 (Perkin), while at a pressure of 40 mm. 
mercury it boils at 89-9° C. The specific gravity is 1-113 at 
20° C, and the vapour density is 4-4. 

On cooling, a crystalline mass melting at — 39° C. is obtained. 

It is insoluble in water, but soluble in most of the organic 
solvents. 

Benzyl chloride is fairly stable to water, and only by prolonged 
boiling with an excess is it decomposed into benzyl alcohol and 
hydrochloric acid : 

C 6 H 5 — CH 2 C1 + H 2 0 -+ C„H 6 — CH 2 OH + HC1. 

By heating for 2 hours with 10 parts of water and 3 parts of 
freshly-precipitated lead hydroxide, benzyl alcohol is also obtained 
according to the equation 2 : 

2C 6 H 6 — CH 2 C1 + Pb(OH) 2 = 2C 6 H 5 — CH 2 OH + PbCl 2 . 

On boiling benzyl chloride with alcoholic potassium 
hydroxide solution or with sodium ethylate, benzyl ethyl ether 
is formed : 

C 6 H 5 CH 2 C1 + C 2 H 5 ONa = C 6 H 5 CH 2 OC 2 H 5 + NaCl. 

This is a liquid boiling at 185 0 C. and volatile in steam. 3 This 
reaction with boiling alcoholic sodium ethylate is quantitative. 4 

Benzyl chloride reacts similarly with other alcoholates and 
with phenates. 

1 Perkin, /. Chem. Soc, 1896, 69, 1203. 

* Lauth, Ann., 1867, 143, 81. 

3 Cannizzaro, Jahresber. fortschr. Chemie, 1856, 581. 

* Ingold, /. Chem. Soc, 1928, 2249. 



BENZYL CHLORIDE : PROPERTIES 



By the action of chlorine on benzyl chloride, in presence of 
iodine as catalyst, />-chlorobenzyl chloride is formed : 

CH 2 C1 CH S C1 




+ CI, 



+ HCl 



CI 

This is a crystalline substance melting at 29° C, soluble in 
alcohol, ether, benzene and acetic acid, but insoluble in water. 
It boils at ordinary pressure at 214° C. 1 

By the action of bromine in the presence of iodine, 
/>-bromobenzyl chloride and />-bromobenzyl bromide are formed. 2 

On passing the vapour of benzyl chloride over a platinum 
wire heated to redness, stilbene and hydrochloric acid are formed. 8 

By the action of mild oxidising agents like calcium nitrate, 
barium nitrate, etc., benzyl chloride is converted into 
benzaldehyde : 

2 C,H S -CH,C1 + Ba(N0 3 ) 2 = 

= BaCl a + 2 C.H5-CHO + NO + NO, -f- H,0 

When strong oxidising agents like chromic acid mixture are 
employed, benzoic acid is formed. 

The action of fuming nitric acid introduces a nitro-group into 
the benzene nucleus and o-nitrobenzyl chloride is formed 4 : 

C 6 H 5 CH 2 C1 + HNO3 = C 6 H 4 (N0 2 )CH 2 C1 + H 2 0. 

This compound is more powerfully lachrymatory than benzyl 
chloride (see p. 135). 

With alcoholic ammonia, a mixture of mono-, di- and 
tri-benzylamines is formed. With hexamethylene tetramine an 
addition product results. 5 

On boiling an alcoholic solution of benzyl chloride with an 
aqueous solution of potassium cyanide, benzyl cyanide is formed 6 : 

C 6 H 6 CH 2 C1 + KCN = C 6 H 5 CH 2 CN + KC1. 

This is a colourless liquid, S.G. 1-0125 at 25 0 C, boiling at 233° C. 
at normal pressure and at 107° C. at a pressure of 12 mm. On 
cooling it solidifies to a crystalline mass, melting at — 24-6° C. 

1 Kuhlberg, Ann., 1868, 146, 320. 

2 Errera, Gazz. Chim. Ital., 1887, 17, 198. 

3 Lob, Ber., 1903, 36, 3060. 

4 Noelting, Ber., 1884, 17, 385. 

6 Sammelt, Compt. rend., 1913, 157, 852. 
* Cannizzaro, Ann., 1855, 96, 247. 

3-2 



132 



AROMATIC ESTERS 



By heating alcoholic solutions of sodium sulphide and benzyl 
chloride together on the water-bath, benzyl sulphide is formed 1 : 

2C 6 H 5 CH 2 C1 + NagS = (C 6 H 5 CH 2 ) 2 S + 2 NaCl. 

This is white and crystalline, insoluble in water and soluble in 
alcohol and ether. On heating to about 120° C. it decomposes 
into hydrogen sulphide, sulphur, toluene, triphenyl butane and 
triphenyl thiophene. 

Sodium sulphide and benzyl chloride also react in aqueous 
solution, but in this case the reaction is much slower. 

Benzyl chloride attacks iron, tin and copper vigorously and 
polymerises in contact with these metals. 

The animal fibres absorb the vapour of benzyl chloride in 
greater quantities than do the vegetable fibres. Following this 
absorption, the resistance of the vegetable fibres is notably 
lowered, while that of the animal fibres is practically unchanged. 
The benzyl chloride vapour is only partly removed by a current 
of air. 2 The limit of insupportability is 85 mgm. per cu. m. of 
air, according to Flury. 

2. Benzyl Bromide. C 6 H 5 — CH-jBr. (M.Wt. 171-01) 

Benzyl bromide was used by the Germans as a war gas in 
March, 1915, but only for a short time owing to the cost and the 
scarcity of the raw material (toluol). Later it was completely 
abandoned, being superseded by other substances with greater 
irritant power. 

Benzyl bromide may be prepared by the action of hydrobromic 
acid on benzyl alcohol 3 or by the action of bromine on toluene. 4 
Stephen 5 has worked out a method which consists in treating 
dibromomethyl ether with benzene : 

2C 6 H 6 + 0(CH 2 Br) 2 = 2 C 6 H 5 — CH 2 Br + H 2 0. 

Laboratory Preparation 

The method of Schramm 6 is usually employed ; this is based 
on the action of bromine on toluene. 

50 gm. toluene are placed in a perfectly dry flask of 250 ml. 
capacity which is fitted with a tap-funnel and a reflux condenser. 
The flask is exposed to direct sunlight and then 75 gm. bromine 
are allowed to enter drop by drop, agitating at the same time. 

1 Maercker, Ann., 1865, 136, 86. 

2 Alexejevsky, /. Prikl. Khim., 1929, 1, 184. 

3 Kekule, Ann., 1866, 137, 190. 

4 Beilstein, Ann., 1867, 143, 369. 

6 Stephen and Short, /. Chem. Soc, 1920, 117, 510. 
« Schramm, Ber., 1885, 18, 608. 



BENZYL BROMIDE 



133 



The solution, which is first coloured reddish-brown, becomes 
colourless as the reaction proceeds. When all the bromine has 
been added, the reaction product is fractionally distilled and the 
fraction boiling between 190° and 205° C. collected separately. 
This is refractionated through a dephlegmator. 

Industrial Manufacture 

Benzyl bromide is prepared on the large scale as in the 
laboratory by the action of bromine on toluene. In this reaction 
half of the bromine is converted into hydrobromic acid : 

C 6 H 5 — CH 3 + Br 2 = C 6 H 6 — CH 2 Br + HBr. 

In order to utilise this bromine, potassium chlorate is added 
to the reaction mixture so as to regenerate the bromine, which 
re-enters the reaction cycle : 

6C 6 H 5 — CH 3 + 3 Br 2 + KC10 3 = 6C 6 H 5 — CH 2 Br + KC1 + 3H 2 0. 

The bromine may also be treated with sodium hydroxide in 
order to prevent the loss of bromine as hydrobromic acid : 

6NaOH + 3Br 2 = 5NaBr + NaBr0 3 + 3H 2 0. 

The mixture of sodium bromide and bromate obtained is then 
agitated with the toluene while a current of chlorine 1 is passed 
into the mixture. 

NaBr0 3 + 5 NaBr + 6 C 6 H 5 -CH 3 + 3 Cl 2 = 

= 6 NaCl + 3 H 2 0 + 6 C 6 H 5 -CH 2 Br 

Physical and Chemical Properties 

Benzyl bromide is a clear, refractive liquid with an 
aromatic odour which boils at 198° to 199° C. at ordinary pressure, 
and at 127° C. 2 at 80 mm. pressure. It solidifies at — 3-9° C. 

Its specific gravity is 1-438 at 16° C. and its vapour density 
is 5-8. The volatility at 20 0 C. is 2,440 mgm. per cu. m. (Miiller). 

It is insoluble in water, but soluble in the common organic 
solvents. 

Benzyl bromide, like the chloride, is decomposed by water 
with difficulty. 3 Only after prolonged boiling (30 hours) of an 
aqueous solution of benzyl bromide is it saponified into 
hydrobromic acid and benzyl alcohol. 

Concentrated nitric acid forms, besides benzoic acid, 
tribromoaniline and tribromoaminobenzoic acid. 4 

1 Libermann, op. cit. 

2 Van der Laan, Chem. Weekblad., 1906, 3, 15. 
8 P. Rona, Z. ges. exp. Med., 1921, 13, 16. 

* Fluerscheim and Holmes, /. Chem. Soc, 1928, 1607. 



134 



AROMATIC ESTERS 



Alcoholic ammonia reacts with benzyl bromide, even in the 
cold, to form tribenzylamine 1 (C 6 H 5 CH 2 ) 3 N. 

Benzyl bromide, when treated with an alcoholic solution of 
silver acetate, separates silver bromide rapidly, even in the cold 
(Kekule). 

In contact with iron it decomposes in a short time. Because 
of this decomposition it must be placed in lead containers if it is 
to be used in projectiles. 2 

During the war a mixture of benzyl bromide, castor oil, alcohol, 
sodium thiosulphate and glycerol was employed. 3 

The minimum concentration of benzyl bromide causing 
irritation is 4 mgm. per cu. m. air. The limit of insupportability 
is 60 mgm. per cu. m. and the mortality product 6,000 (Muller) . 

3. Benzyl Iodide. C„H 8 — CH 2 I (M.Wt. 218-01) 

This substance, which has well-known lachrymatory properties, 

may be obtained according to Cannizzaro 4 by the action of 

phosphorus iodide with benzyl alcohol or by the action of 

potassium iodide on benzyl chloride or bromide. 

According to some authors, benzyl iodide was used as a war 

gas by the French in March, 1915. 

Laboratory Preparation 5 

150 ml. 95% ethyl alcohol, 20 gm. benzyl bromide and 25 gm. 
potassium iodide are placed in a flask of 250-300 ml. capacity 
fitted with a reflux condenser. This is then warmed on the 
water-bath to 50° to 60° C. with continual agitation. After 
heating for half an hour, the product is poured into 150 ml. 
water, the oily layer separated, washed with water and 
crystallised by means of a freezing mixture. The crystals are 
collected and purified by crystallisation from alcohol. 

Physical and Chemical Properties 

Benzyl iodide forms colourless crystals melting at 24-1° C. 
The liquid has a specific gravity of 17735 at 25° C. and boils with 
decomposition at 226° C. (Lieben). 6 The vapour density is 7-5. 
It is insoluble in water, soluble in alcohol, ether and benzene and 
slightly soluble in carbon disulphide (Kumpf) . 

Benzyl iodide has a volatility of 1,200 mgm. per cu. m. of air. 

1 Kekule, Ann., 1866, 137, 190. 

* Alexejevsky and coll., /. Prikl, Khim., 1928, 1, 194. 

8 S. de Stackelberg, Le piril chimique et la croxx vxolette. Lucerne, 1929. 

* Cannizzaro, Gmelins Handbuch, 6, 38. 

* Meyer, Ber., 1877, 10, 311 ; Kumpf, Ann., 1884, 224, 126. 

* Lieben, Jahresber. Fortschr. Chem., 1869, 425. 



o-NITROBENZYL CHLORIDE 



135 



Like the two previous compounds, it is decomposed by water 
with difficulty. 1 

Crystals of benzyl iodide when gently heated become red in 
colour owing to incipient decomposition. By the action of silver 
acetate in presence of acetic acid, silver iodide and benzyl acetate 
are formed (Lieben). 

It reacts easily with tertiary amines, forming quaternary 
ammonium iodides. 2 

It may be classed among the strongest lachrymators. The 
lower limit of irritation is 2 mgm. per cu. m. of air (Miiller). The 
maximum concentration which a normal man can support for a 
period of not more than 1 minute is 25-30 mgm. per cu. m. 
Mortality-product : 3,000 (Miiller). 



4. Ortho-nitrobenzyl Chloride (M.Wt. 171*55) 

C 6 H 4 < 



XH 2 C1 

/ 



* X N0 2 

Ortho-nitrobenzyl chloride was prepared in 1883 by Abelli, 3 
together with the meta-compound, by the reaction of concentrated 
nitric acid on benzyl chloride. It may also be obtained, according 
to Haussermann and Beek, 4 by the action of chlorine at 130° to 
140° C. on a mixture of 2 parts of o-nitrotoluene and 1 part 
sulphur. 

According to Lindemann, 5 it was used by the French during 
the war mixed with ^>-nitro benzyl chloride under the name of 
" Cedenite." 

Physical and Chemical Properties 

o-Nitrobenzyl chloride forms crystals with a melting point of 
48° to 49 0 C. It is purified by crystallisation from ligroin. Its 
vapour density is 5-9. It is insoluble in water, but easily soluble 
in cold benzene and in ether and alcohol on warming. 

With potassium iodide it is easily converted into o-nitrobenzyl 
iodide, 6 and an alcoholic solution of potassium cyanide converts 
it into o-nitrobenzyl cyanide. 7 Potassium permanganate oxidises 
it to o-nitrobenzoic acid. 

The lower limit of irritation is i-8 mgm. per cu. m. of air 
(Lindemann). It has a vesicant action. 

1 P. Rona, Z. ges. exp. Med., 1921, 13, 16. 

2 Vedekind, Ann., 1901, 318, 92. 

3 Abelli, Gazz. chim. Ital., 1883, 13, 97. 

* Haussermann and Bbek, Ber., 1892, 25, 2445. 

4 Lindemann, Toksykologya chem. srodkow bojowych, Warsaw, 1925 
« Kumpf, Ann., 1848, 224, 103. 

' Bamberger, Ber., 1886, 19, 2635. 



136 



AROMATIC ESTERS 



5. Xylyl Bromide. C 6 H 4 (CH 3 )CH a Br. (M.Wt. 185) 

Xylyl bromide was prepared in 1882 by Radziszevsky. 1 It 
was used for the first time as a war gas in January, 1915, but 
its use was abandoned towards the end of the war because of the 
ease with which it was dealt with by the ordinary carbon filters 
and of the inconvenience caused by its attack on iron containers. 
It is also known as " T-Stoff." 

Xylyl bromide may be easily prepared by the reaction of 
bromine on commercial xylol. 2 This reaction is carried out either 
by heating the xylol to 115° C. or by exposing the reaction-mass 
to the action of a light source rich in ultra-violet radiations and 
keeping the temperature at 50° to 60° C. 3 

In both cases the following reaction takes place : 

/CH 3 /CH 3 
C 6 H 4 ( + Br 2 = HBr + C 6 H 4 ^ 

CH 3 CH 2 Br 

Since commercial xylol is a mixture of the three isomeric 
xylenes, ortho, meta and para, the method of bromination 
mentioned above produces a mixture of the three derivatives : 



CH,Br 
/\CH 3 



o-xylyl bromide 



CH 2 Br 



wi-xylyl bromide 



CH 2 Br 



^CH, 

/i-xylyl bromide 



All these three compounds have lachrymatory properties. 

In the bromination of xylol a secondary reaction also takes 
place ; this is the conversion of xylyl bromide into xylylene 
bromide, due to the tendency of bromine to react with xylyl 
bromide as well as with the xylol also present. 



CH 2 Br 

/N.CH, 



+ Br, 



CH 2 Br 
/NcHsBi 



+ HBr 



1 Radziszevsky and Wispek, Ber., 1882, 15, 1747. 

2 Atkinson and Thorpe, /. Chem. Soc, 1907, 91, 1695. 

8 Schramm, Ber., 1885, 18, 1278 ; Farbenfabr. F. Bayer, D.R.P., 
Chem. Zentr., 1921 (II), 803. 



297933 i 



XYLYL BROMIDE: PREPARATION 



Laboratory Preparation 

It is prepared by the action of bromine on xylol. 500 gm. 
commercial xylol are placed in a 1 -litre flask which is closed with 
a stopper carrying three holes. Through one of these passes a 
thermometer whose bulb is immersed in the reacting liquid, 
through the second the stem of a tap-funnel, and through the 
third a reflux condenser which leads by means of a tube bent at 
right angles to a dish containing water. 

The flask is heated so as to raise the temperature of the liquid 
to about 115° C. and to keep it as near this temperature as possible 
while bromine is dropped in slowly (about 4 drops a second) 
from the tap-funnel, into which 500 gm. bromine have been 
previously measured. This quantity of bromine is about a 
quarter less than the theoretical. 

Each drop of bromine reacts immediately it enters the xylol, 
which becomes slightly coloured, while the hydrobromic acid 
which is formed bubbles out and passes through the condenser to 
the water in the dish, where it dissolves. 

When all the bromine has been dissolved (about 2 hours), the 
heating to 115 0 to 120° C. is continued until all the hydrobromic 
acid has been driven off from the reaction mixture. At the end 
of this evolution of gas, the flask is cooled and its contents 
transferred to a distillation flask. On distillation, the first 
fraction between 140° and 200° C. is collected separately. This 
contains the xylol which has not reacted and any hydrobromic 
acid which remained behind. At 210° C. the mixture of the three 
xylyl bromides begins to distil. When the thermometer reaches 
230° C. the distillation is stopped ; the flask contains a black oily 
residue. In order to obtain a purer product, the fraction collected 
between 210 0 and 230° C. may be redistilled. The yield is about 

75%. 

Industrial Manufacture 

In the manufacture of xylyl bromide in Germany, enamelled 
vessels fitted with agitators and cooling coils were employed, 
according to Norris. 1 

The required quantity of xylol was poured into these vessels, 
heated to 115° C. and then about three-quarters of the theoretical 
bromine added in small quantities so that at the end of the 
reaction some unchanged xylol still remained. The hydrobromic 
acid evolved was absorbed in special towers. 

At the end of the operation the product was distilled under 



1 Norris, /. Ind, Eng. Chem., 1919, 11, 828. 



138 



AROMATIC ESTERS 



reduced pressure. After the xylol had been recovered, the residue 
was employed without rectification or purification. 

Physical and Chemical Properties 

In the pure state it is a colourless liquid boiling between 
210° and 220° C, with a density of 1-4, and has an aromatic 
odour, which when much diluted is reminiscent of elder blossom. 

The volatility at 0° C. is 140 mgm. per cu. m. of air, and at 
20° C. is 600 mgm. per cu. m. 

It is slowly decomposed by water, like benzyl iodide. 1 The 
crude product energetically attacks iron and so must be stored 
in lead-lined containers. 

The minimum concentration capable of provoking irritation 
is i-8 mgm. per cu. m. The limit of insupportability is 15 mgm. 
per cu. m. The mortality-product is 6,000 according to Miiller. 
However, according to Prentiss it is 56,000. 

Analysis of the Aromatic Esters 

Detection 

The aromatic esters are identified by saponifying them with 
alcoholic potash and then examining the product for the halogen 
hydroacids with silver nitrate solution. 2 

Detection of Benzyl Chloride. Benzyl chloride, on heating 
under reflux with a solution of lead nitrate, forms benzaldehyde 
which is easily recognised by its almond-like odour. 

Another method of detecting benzyl chloride, according to 
Lob, 3 consists in passing the vapour of the substance to be 
examined over a platinum wire heated to redness and then 
testing for hydrochloric acid in the product with silver nitrate. 

Detection of Benzyl Bromide. According to Kekul£, 4 when 
benzyl bromide is treated with an alcoholic solution of silver 
acetate, a yellow precipitate of silver bromide rapidly separates 
even in the cold. 

Quantitative Determination 

The quantitative determination of the aromatic esters is best 
carried out by the same reactions given above for their detection. 

Determination of Benzyl Chloride. Benzyl chloride may be 
determined, according to Schulze, in the following manner 8 : 

1 Rona, Z. ges. exp. Med., 1921, 13, 16. 

! Weston, Carbon Compounds, London, 1927, 21, 

* Lob, Ber., 1903, 36, 3060. 

* Kekule, Ann., 1866, 137, 191. 

6 K. Schulze, Ber., 1884, 17, 1675. 



AROMATIC ESTERS: ANALYSIS 



139 



about 2 gm. of the substance to be examined are accurately 
weighed into a flask fitted with a reflux condenser, excess of 
an alcoholic solution of silver nitrate, saturated in the cold, is 
added and then the whole is heated to boiling for about 5 minutes. 
At the end of the reaction, the precipitate formed is filtered on a 
weighed Gooch crucible, washed first with alcohol, then with 
hot water slightly acidified with nitric acid and then again with 
alcohol. The crucible is heated, first gently, then to red heat and 
reweighed. From the gain in weight the quantity of benzyl 
chloride in the sample may be calculated. 

Determination of Benzyl Bromide. The determination of this 
substance may be carried out by the method already described 
for benzyl chloride. However, according to Van der Laan, 1 it is 
sometimes more convenient to decompose the substance directly 
with a measured volume of standardised alcoholic silver nitrate 
solution and to titrate the excess of the latter with ammonium 
thiocyanate solution by the Volhard method. 

Determination of Benzyl Iodide. The following method may be 
employed for the quantitative determination of benzyl iodide : 

About 2 gm. benzyl iodide are weighed into a flask and then 
50 ml. 20% alcoholic potash solution are added and the mixture 
refluxed for about an hour. At the completion of the saponifica- 
tion the contents of the flask are allowed to cool and then 
transferred to a 500-ml. flask and made up to volume with water. 
100 ml. of the resulting solution are placed in a distillation flask 
and distilled in steam after adding 10 gm. ferric ammonium alum 
and acidifying with sulphuric acid. By this treatment, the ferric 
salt is converted to the ferrous condition, liberating iodine which 
is distilled over into 5% potassium iodide solution. At the end of 
the distillation, the free iodine in the potassium iodide solution is 
titrated with a decinormal solution of sodium thiosulphate. 
From this, the amount of iodine and so the quantity of benzyl 
iodide in the sample may be calculated. 

1 Van der Laan, Rec. trav. Chim., 26, 54. 



CHAPTER X 



ALDEHYDES 

Acrolein was the only aldehyde used as a war gas during the 
war of 1914-18, and its use was very limited as it was soon 
superseded by other substances having superior offensive 
properties. 

In the post-war period several halogenated derivatives of 
acrolein have been examined ; for example, monochloroacrolein, 1 
CH 2 = CC1.CHO, a colourless liquid, boiling at 29 0 to 31 0 C. at a 
pressure of 17 mm. of mercury and having S.G. 1-205 at 15 0 C, 
is both lachrymatory and vesicant in its action. Also some of 
the homologues of acrolein, like crotonic aldehyde, and its 
monochloroderivative, CH 3 — CH = CC1 — CHO, a colourless liquid, 
boiling at 146° C, and having a specific gravity of 1-422 at 15° C. 
This has toxic and lachrymatory properties inferior to those of 
chloropicrin, however. 2 

Acrolein. CH 2 = CH— CHO. (M.Wt. 56) 

Acrolein, or acrylic aldehyde, was prepared by Redtenbacher 
in 1843, 3 and was first used as a war gas by the French in 1916, 
being suggested by Le Pape, whence its name of " Papite." 
However, it was not very efficient, chiefly because of its tendency 
to polymerise into substances having no irritant action. 

Acrolein is usually obtained from glycerol by abstraction of 
2 molecules of water : 

CH 2 OH 
I 

CHOH 
CH 2 OH 

The following may be employed as dehydrating agents : 
phosphoric acid, boric acid, potassium bisulphate, sodium 
sulphate, etc. However, the preparation of acrolein is not very 
satisfactory when these substances are used, the yield being not 
above 30-40% of the theoretical. It was only as a result of the 

1 Moureu and coll., Ann. Mm., 1921, 15, 158. 

8 Moureu and coll., Bull. soc. Mm., 1921, [4] 29, 29. 

3 Redtenbacher, Ann., 1843, 47, 114. 

140 



CH, 
CH 



H 



+ 2 H 2 0 



ACROLEIN : PREPARATION 



141 



studies of Moureu 1 on this subject that it was possible to obtain 
higher yields. In his method a mixture of 5 parts potassium 
bisulphate and 1 part potassium or sodium sulphate is used. 

Little is known concerning the action of the acid sulphates on 
glycerol. A recent theory suggests that salts of glycero-sulphuric 
acid are first formed : 



CH 2 OH CH 2 OH 
HOH + 2 KHS0 4 = 2 H 2 0 + CHO • S0 3 K 
H 2 OH CH 2 0 • SO3K 



On heating, these are thought to decompose forming sulphuric 
acid again and acrolein : 



CH 2 OH 



CH, 



CHO • SO3K = 2 KHS0 4 + CH 



CH 2 0 • SO3K 



CHO 



Laboratory Preparation 2 

100 gm. glycerol, 80 gm. potassium bisulphate and 20 gm. 
anhydrous sodium sulphate are placed in a flask A of about 
1 litre capacity, which is fitted with a tap-funnel and connected 
by means of a glass tube (see Fig. 9) with another flask B of the 




Fig. 9. 

same size, this being also connected to a Liebig condenser. The 
first flask is immersed in an oil bath and heated to 160 0 to 180° C. 
The products of the reaction — water, acrolein, etc. — pass over 

1 Moureu, Compt. rend., 1919, 169, 621, 705, 885 and 1068 ; Bull. soc. chim., 
1920, 27, 297. 

* Nekrassov, op cit. ; E. Zappi, Anales A soc. Quim. Argentina, 1930, 18, 243, 



142 



ALDEHYDES 



into the flask B in which 1 gm. hydroquinone has been placed. 
When the acrolein commences to distil, a further 100 gm. glycerol 
are slowly run into A from the tap-funnel and the reaction 
continued for 4-5 hours by heating to about 250 0 C. at the end. 
In the receiver B a liquid collects which separates into two layers ; 
the lower of these is an aqueous solution of acrolein and the upper 
a solution of water in acrolein. The upper layer is separated off, 
washed with soda solution, dried over fused calcium chloride and 
distilled. 

It is advisable to add o-i-o>2 gm. hydroquinone in order to 
retard polymerisation. 

Industrial Manufacture 

The industrial manufacture of acrolein is carried out in 
cylindrical iron vessels of about 30 cm. diameter fitted with 
agitators and closed by a lid having three holes, through one of 
which the glycerol is introduced, through the second passes a 
thermometer and through the third a condenser leading to a large 
flask heated on a water-bath. This flask is also fitted with a 
thermometer and may be connected to another condenser, cooled 
by water. 

In the iron vessel 2 kgm. potassium bisulphate and 400 gm. 
potassium sulphate are placed, while 600 gm. glycerol of 28° Be. 
are run in. The whole is then heated in an air-bath until the 
temperature inside the vessel reaches ioo° C, when the reaction 
commences and a mixture of water and acrolein begins to distil. 
The temperatures in the first condenser and in the flask are then 
so regulated that the mixture of vapours enters the second 
condenser at a temperature of about 70° C. A considerable 
proportion of the water and compounds with higher boiling points 
is thus condensed in the flask while the acrolein, together with 
the remaining water vapour condenses in the second condenser 
and is collected in the appropriate receiver. 

When only a little glycerol remains in the iron vessel, more is 
added at such a rate that the speed of distillation is not diminished. 

The internal temperature should be maintained throughout 
the reaction at 195° C. 

The crude acrolein obtained is dried over calcium chloride and 
redistilled. The yield is 60-65% of theoretical (Moureu). 

Physical and Chemical Properties 

In the pure state acrolein is a clear liquid boiling at 52 0 C. and 
solidifying at — 88° C. Its specific gravity is o-86 at 15° C, and 
its vapour density is 1-94. Its volatility at 20° C. is 407,000 mgm. 



ACROLEIN : PROPERTIES 



143 



per cu. m. It is somewhat miscible with water (1 part of acrolein 
is miscible with 2-3 parts water) 1 and with most of the organic 
solvents. 

Acrolein is a substance which alters easily and in it the 
characteristic properties of the aldehydes — the tendencies to 
polymerisation and oxidation — are very pronounced. Polymerisa- 
tion transforms acrolein into an amorphous white mass, insoluble 
in water and alcohol, which no longer has the irritating properties 
of acrolein and is known as " disacryl." In order to prevent, or 
rather retard, this polymerisation the acrolein should be left in a 
somewhat impure condition, as it seems that the impurities have 
the property of inhibiting the change. Substances which have 
been found to be especially good stabilisers for acrolein are phenol, 
hydroquinone, benzoic acid, etc., which even if present to the 
extent of 1-2% check the polymerisation for many months 
(Moureu) . 

Among the reactions of acrolein which are important in 
determining its structural formula are those in which it is reduced 
to allyl alcohol and to propionaldehyde or oxidised to acrylic acid. 
Reduction is most conveniently carried out by means of aluminium 
amalgam, 2 while atmospheric oxygen is sufficient to oxidise it. 
More powerful oxidants cause profound breakdown of the 
molecule ; thus nitric acid forms oxalic and glycollic acids and 
chromic acid mixture formic acid and carbon dioxide. 

Because of the presence of a double link and an aldehyde 
group in its molecule, acrolein forms two different types of 
compounds, according to whether the double link or the aldehyde- 
oxygen takes part in the reaction. Thus, with the halogens or 
the halogen hydroacids, the following take place : 

CH,=CH-CHO + Br 2 = CH 2 Br-CHBr-CHO 
CH.=CH-CHO 4- HC1 = CH 2 Cl-CH.,-CHO 

while with acetic anhydride 

/COCH3 /OCOCH3 
CH 2 =CH-CHO + 0< = CH 2 =CH-CH( 

N COCH 3 N OCOCH 3 

With sodium bisulphite, reaction takes place both with the 
unsaturated carbon atoms and with the aldehyde group 3 : 

/OH 

CH 2 =CH-CHO + 2 NaHS0 3 = CH 2 (S0 3 Na)CH 2 -CH< 

N S0 3 Na 

1 Geuther, Ann., 1859, 112, 10. 

a Harries and Haga, Ann., 1904, 330, 226. 

3 M. Muller, Ber., 1873, 6, 1445. 



144 



ALDEHYDES 



Water reacts with acrolein only at ioo°, forming the correspond- 
ing hydroxy-aldehyde : 

CH 2 = CH— CHO + H 2 0 = CH 2 OH— CH 2 — CHO. 

Alkalies rapidly polymerise acrolein. 1 An ethereal solution of 
potassium cyanide in presence of acetic acid forms the nitrile of 
a hydroxy vinylacetic acid 2 : 

CH 2 = CH— CHO + HCN = CH 2 = CH— CHOHCN 

This is a colourless liquid, boiling at 93 0 to 94° C. at 16 mm. of 
mercury. Its density at I5°C. is 1-009, and it is miscible in all 
proportions with alcohol, ether and water, but sparingly soluble 
in petroleum ether. 

Pure acrolein does not attack metals. 

The minimum concentration of acrolein which causes lachryma- 
tion is 7 mgm. per cu. m. of air. The limit of insupportability is 
50 mgm. per cu. m. The mortality-product is 2,000 according to 
Miiller, and 7,000 according to Meyer. 

Detection 

Lewin's Reactions? On treatment of acrolein with a solution 
of sodium nitroprusside in piperidine, an intense blue coloration 
is produced which passes to violet with ammonia and to brown 
with mineral acids. The same colour changes are produced by 
bubbling air containing acrolein vapour through the reagent. 
Sensitivity : 25 mgm. acrolein per cu. m. of air. 4 Instead of 
piperidine, dimethylamine may be employed, but the sensitivity 
of the reaction is then less. 

Nierenstein' s Reaction. 5 This reaction is based on the change 
of colour of a solution of phloroglucinol in presence of acrolein. 
On treatment of the solution to be tested with 2-3 ml. 5% 
phloroglucinol and addition of 5-10 drops of alkali, and then 
boiling rapidly, the presence of acrolein is detected by a bluish- 
green colour. 

p-Nitro Phenylhydrazine Reaction* An aqueous solution of 
^-nitro phenylhydrazine hydrochloride, which should remain 
colourless on addition of a few drops of acetic acid, produces an 
orange-yellow precipitate with acrolein. This precipitate consists 
of small stellar crystals, easily visible under the microscope. 

1 Nef, Ann., 1904, 335, 220. 

1 Lobry de Bruyn, Rec. trav. ckim., 1885, 4, 223 ; V. der Sleen, Rec. trav. 
chim., 1902, 21, 211. 

3 Lewin, Ber., 1899, 32, 3388. 

4 Grodsovsky, Analis Voxduxa, Moscow, 1931, 206. 

5 Nierenstein, Collegium, 1905, 158 ; Chem. Zentr., 1905 (II), 169. 

6 H. Behrens, Chem. Ztg., 1905, 27, 1105. 



ACROLEIN : DETERMINATION 145 



Quantitative Determination 

Ivanov's Method. 1 This is founded on the reaction of acrolein 
with sodium bisulphite already mentioned. The excess bisulphite 
is titrated with iodine according to the following equations : 

CH 2 =CH-CHO + 2 NaHSOs = CH 2 (S02Na)-CH 2 -CH(OH)S0 3 Na 
NaHS0 3 + I 2 + H 2 0 = NaHSO, + 2 HI 

o-i-o-i5 gm. of the substance to be analysed is placed in a 
small glass bulb which is then sealed in the blowpipe and weighed. 
The bulb is placed in a bottle together with 100 ml. water. The 
bulb is then broken and a standardised solution of sodium 
bisulphite added, sufficient being employed to react with 50% 
more acrolein than is actually present in the sample. The 
mixture is allowed to stand for about 6 hours and then the excess 
of bisulphite is titrated with iodine solution in presence of starch, 
to a blue coloration stable for 15 minutes. 

The bisulphite and iodine solutions are standardised so that 
1 ml. of each is equivalent to 1 mgm. acrolein. 

This method has also been suggested by Zappi. 2 

1 N. Ivanov, Arch. Hyg., 1911, 74, 307. 

2 E. Zappi and Labriola, Anales Asoc. Quim. Argentina, 1930, 18, 243. 



CHAPTER XI 



HALOGENATED KETONES 
(A) ALIPHATIC 

In the ketone group, the halogenated derivatives are of great 
interest as war gases. 

They are usually prepared by the direct action of the halogens 
on the corresponding ketones. The introduction of a halogen 
atom into the molecule of a ketone usually takes place according 
to a definite rule : The first halogen atom entering substitutes a 
hydrogen of the least hydrogenated alkyl group, whether 
secondary or tertiary, and it is only the second halogen atom 
which can enter a different group. 

For example, in chlorinating methyl ethyl ketone, 
CH 8 — CO— CH 2 — CH 3 , methyl-a-chloroethyl ketone is first 
obtained : 

CH3-CO-CH-CH3 

da 

and then on further, chlorination, methyl-a-/?-dichloroethyl 
ketone : 

CH 3 -C0-CH-CH 2 C1 
CI 

The introduction of-a second halogen atom into the molecule 
of these substances affects their properties differently according 
to the position it occupies. It is found that the symmetric 
dihalogenated ketones have higher specific gravities, higher 
boiling points and, in particular, more powerful toxic properties 
than the asymmetric dihalogenated ketones. Thus in chlorinating 
acetone, chloroacetone is first obtained, CH 2 C1 — CO — CH 3 , and 
then by further chlorination a mixture of the symmetric and 
asymmetric dichloro-derivatives is obtained : 

CH 2 C1— CO— CH 2 C1 and CHC1 2 — CO — CH 3 . 

On examining these two compounds, 1 it is found that the 
symmetric compound (S.G. 1-383 and b.p. 171° C.) is more toxic 

1 T. Posner and K. Rohde, Ber., 1909, 42, 3233. 
146 



ALIPHATIC HALOGENATED KETONES 



than the asymmetric derivative (S.G. 1-236 and b.p. 120° C.). 1 
Symmetric dichloroacetone, besides its normal irritant action on 
the eyes and the respiratory organs, has, even in low concentra- 
tions, an irritant action on the skin which is more precisely termed 
" orticant " action. 2 

In the preparation of the halogenated ketones by direct 
halogenation only half the halogen reacting enters the ketone 
molecule, the other half forming the halogen hydracid : 

CH 3 — CO — CH 3 + Br 2 = CH 3 — CO— CH 2 Br + HBr. 

In order to prevent this loss of halogen, especially in the 
industrial manufacture of the bromo- and iodo- derivatives, the 
halogen of the hydracid is regenerated by adding to the reaction 
mixture an oxidising agent, usually sodium chlorate. By reaction 
with the hydracid this liberates the halogen which can re-enter 
the reaction : 

NaC10 3 + 6HBr = 3Br 2 + 3H 2 0 + NaCl. 

The halogenated aliphatic ketones are, in general, somewhat 
unstable compounds. In time, decomposition or resinification 
takes place. These processes are partly prevented by the addition 
of stabilising substances which impede the changes for some 
time. 

Because of the presence of the carbonyl group in the molecule, 
they react with sodium bisulphite to form well-crystallised 
additive products. This behaviour is employed in practice to 
separate the halogenated ketones from the secondary products 
of the reaction. 

The halogenated ketones have powerful lachrymatory 
properties. The iodine compounds are the most irritant, then 
following the bromine and lastly the chlorine. 

During the war of 1914-18, bromoacetone and bromomethyl 
ethyl ketone were especially used. Chloroacetone was employed 
only for a short time, being soon superseded by other substances 
having a more powerful aggressive action. 

Since the war several other halogenated ketones have been 
prepared and examined, such as 

x'-P-dichloromethyl ethyl ketone, C1CH 2 — CO — CH 2 — CF^Cl, 

obtained by the action of ethylene on chloroacetyl chloride in 
presence of aluminium chloride, or, in better yield, by the action 
of diazomethane on ^-chloropropionyl chloride and then treat- 

1 Lindemann, Toksykologya chem. srodkow bojowch, Warsaw, 1925, 381. 
* Hackmann, Chem. Weekblad., 1934. 31, 366. 



148 



HALOGEN ATED KETONES 



ment with hydrochloric acid. It is a liquid boiling at 65 0 C. at a 
pressure of 3 mm. and has strong lachrymatory properties. 1 

Fluoroacetone, obtained by the action of thallium fluoride on 
bromoacetone, 2 is a yellow liquid boiling at 72-5° C. It has a 
density of 0-967 at 20° C. It is described as having a pungent 
odour, but nothing has been reported concerning its aggressive 
action. 

1. Chloroacetone. C1CH 2 — CO — CH 3 (M.Wt. 92 5) 

Chloroacetone was obtained by Riche in 1859 3 in electrolysing 
a mixture of hydrochloric acid and acetone. It was used in the 
last war, especially by the French, to replace bromoacetone 
during the period of bromine shortage (1914-15) . 

Laboratory Preparation 4 

It is prepared bythe action of chlorine on acetone. 

80 gm. acetone and 20 gm. calcium carbonate in lumps are 
placed in a wide-necked flask fitted with a three-holed stopper. 
Through one of the holes in the stopper a reflux condenser passes, 
through the second a tap-funnel and through the third a delivery 
tube for the chlorine. The calcium carbonate is added in order 
to neutralise the hydrochloric acid liberated in the reaction. A 
current of chlorine is passed in from a cylinder, and 30-40 ml. 
water are gradually added from the tap-funnel. The temperature 
is raised to 60° C. on a water-bath. When the calcium carbonate 
in the flask is almost exhausted, the current of gas is stopped and 
the mixture allowed to stand overnight. The liquid then settles 
into two layers ; the top layer is separated and fractionally distilled. 

Physical and Chemical Properties 

Chloroacetone is a clear liquid boiling at 119° C. It is sparingly 
soluble in water, but easily in alcohol, ether, chloroform and other 
organic solvents. Its specific gravity is 1-162 at 16° C, and its 
vapour density is 3-2. It is relatively slightly volatile : its 
volatility at 20° C. is about 61,000 mgm. per cu. m. (Libermann). 

On exposure to light in sealed glass containers it is converted 
in about 1 year into a solid carbonaceous substance which fumes 
in air giving off hydrochloric acid, and does not react with 
phenylhydrazine, hydroxylamine or oleum, but dissolves in 
fuming nitric acid. 5 

1 R. Carroll and Smith, /. Am. Chem. Soc, 1933, 55, 370. 

2 P. Ray and coll., /. Indian Chem. Soc, 1935, 12, 93. 

3 Riche, Ann., 1859, 112, 321. 

* P. Fritsch, Ber., 1893, 26, 597. 

5 Giua and Rocciu, AM accad. sci. Torino, 1932, 67, 409. 



CHLORO ACETONE : PROPERTIES 



149 



When the vapour of chloroacetone is passed through a tube 
heated to 450° C, acetone, acetaldehyde and crotonaldehyde are 
formed. 1 

Chloroacetone does not react with water. 2 Chlorine even in 
the cold converts it into more highly chlorinated compounds ; 
treatment at ioo° C. in sunlight converts it into pentachloro- 
acetone of the formula 3 CHCLj — CO — CC1 3 . Bromine is almost 
without action in the cold, but on heating to about 100° C. it 
reacts vigorously forming chlorotribromoacetone. 4 Potash 
decomposes chloroacetone, forming potassium chloride and red or 
brown products whose composition has not yet been determined. 5 

The manner in which chloroacetone reacts with other 
compounds is also interesting. With gaseous ammonia, for 
example, aminoacetone is formed, 6 and with nascent hydrogen 
(from zinc and acetic acid) it is converted into acetone. 7 Damp 
silver oxide oxidises it to glycollic, formic and acetic acids. On 
combination with sodium bisulphite, acicular crystals are formed, 
probably of an additive compound of the formula 8 : 



An additive compound is also formed with hexamethylene 
tetramine ; this consists of crystals melting at 122° C. (Nef). 

By the action of sulphuretted hydrogen or sodium sulphide on 
chloroacetone, diacetonyl sulphide is formed : 

2CH 2 C1— CO— CH 3 + Na 2 S = (CH 3 — COCH 2 ) 2 S + 2 NaCl. 

This forms crystals melting at 47° C. and boiling at 136° to 
137° C. at 15 mm. mercury pressure. 

Chloroacetone reacts with hydrocyanic acid, forming chloro- 
acetone chlorohydrin 9 : 

CH 3 — CO — CH 2 C1 + HCN = CH 8 C(OH)(CN)— CH a Cl. 

With potassium cyanide, cyanoacetone is not formed, but 
various polymerisation products are produced. 



1 Nef, Ann., 1904, 335, 278. 

2 Linnemann, Ann., 1865, 134, 171. 
8 Fritsch, Ber., 1893, 26, 597- 

• Cloez, Ann. chim. phys., 1886, [6] 9, 207. 
6 Mulder, Bet., 1872, 5, 1009. 

• G. Pinkus, Ber., 1893, 26, 2197. 
' Linnemann, loc. cit. 

8 Nekrassov, op, cit. 

• Bischof, Ber., 1872, 5, 864. 



CH,C1 



< 



-OH 




i5o 



HALOGEN ATED KETONES 



Chloroacetone decomposes in contact with iron and cannot be 
loaded directly into projectiles. 

The lowest concentration producing irritation of the eyes is 
18 mgm. per cu. m. of air. The limit of insupportability is 
100 mgm. per cu. m. and the mortality-product is 3,000 (Miiller). 

2. Bromoacetone. BrCH 2 — CO— CH 3 (M.Wt. 136 5) 

Bromoacetone was prepared by Linnemann 1 in 1863, and 
because of its powerful lachrymatory properties was used by the 
Germans in 1915 in shells and hand-bombs. 

Laboratory Preparation 

This compound is obtained in a similar manner to chloroacetone, 

by the action of bromine on 
acetone. 

30 gm. acetone, 30 gm. 
acetic acid and 120 ml. water 
are placed in a flask of 250- 
300 ml. capacity which is 
fitted with a reflux condenser 
and a tap-funnel (Fig. 10). 
The whole is heated on a 
water-bath to 70 0 C. and then 
91 gm. bromine are added 
from the tap-funnel, the flask 
being exposed to the direct 
light from a 750-watt lamp. 
When the liquid is decolour- 
ised 60 ml. of water are added, 
the flask cooled anda saturated 
solution of soda added. An oil 
separates and this is dried and 
distilled in vacuo. 

Bromoacetone may be also 
obtained in the laboratory by 
the action of bromine dissolved in acetone on an aqueous solution 
of sodium bromate and sulphuric acid at 30 0 to 35°C. 2 The 
following reaction then takes place : 

10 CH 3 — CO-CH 3 + 4 Br 2 + 
+ 2 NaBr0 3 + 2 HjSO, = 
= 10 CHa-CO-CHjjBr + 
+ 2 NaHS0 4 + 6 H 2 0 

1 Linnemann, Ann., 1863, 125, 307. 

* A. Chrzaszczevska and W. Sobieransky, Roczniki Chem., 1927, 7, 79. 




BROMOACETONE : MANUFACTURE 151 



Industrial Manufacture 

French Method. Because of the limited availability of bromine 
the manufacture of bromoacetone was carried out in France 
during the war by treating acetone with sodium bromate and 
sodium chlorate in presence of sulphuric acid instead of by the 
direct action of bromine on acetone. The following reaction 
takes place : 



NaC10 3 + 3 NaBr + 3 CH 3 -CO-CH 3 + 3 H 2 S0 4 = 



= 3 CH 2 Br-CO-CH 3 + 3 NaHS0 4 + NaCl -f 3 H 2 0 

In this method, if the solution remains acid, hydrochloric acid 
is formed and this reacts with the sodium chlorate, liberating 
chlorine : 

HC10 3 + 5HCI = 3C1 2 + 3H 2 0. 

Hence there is simultaneous chlorination and bromination of 
the acetone, with the formation of a mixture of bromoacetone and 
chloroacetone. 

German Method. The manufacture of bromoacetone in 
Germany 1 was carried out by treating an aqueous solution of 
sodium or potassium chlorate with acetone and then adding in 
small quantities the proper quantity of bromine. 

The reaction is carried out in iron vessels A (Fig. 11) of 
4-5 cu. m. capacity (900- 
1,100 gallons) coated in- 
ternally with resistant tiles 
and fitted with an agitator 
D. These are set in a 
wooden framework E. 

The aqueous solution of 
sodium chlorate is first 
prepared, the acetone is 
added, and then the 
bromine introduced slowly, 
stirring and maintaining the internal temperature at 30° to 40° C. 
At the end of the reaction the oily layer is separated and 
transferred to a vessel where it is treated with magnesium oxide 
to neutralise the excess of free acid. 

In order to determine the quantity of bromoacetone formed, a 
part of the product is dried with calcium chloride and distilled. 
If more than 10% of the product distils below 136 0 C. the product 
is brominated further, if less than 10% then the operation is 
considered satisfactory. The product is stored with the addition 

1 Norris, /. Ind. Eng. Chem., 1919, 11, 828. 




Fig. 11. 



152 



HALOGEN ATED KETONES 



of about i part of magnesium oxide to 1,000 parts of bromoacetone 
in order to neutralise the hydrobromic acid slowly formed on 
storage. 

Physical and Chemical Properties 

Pure bromoacetone is a colourless liquid with a pungent odour 
and a boiling point of 23-5° C. to 24-5° C. at 3-5 mm. mercury and 
31-4° C. at 8 mm. mercury pressure. At ordinary pressure it 
boils at 136° C. with partial decomposition, hydrobromic acid 
and a resinous residue slightly soluble in water and alcohol being 
formed. On cooling strongly it solidifies to a mass which melts 
at — 54 0 C. Its specific gravity at 0° C. is 1-631, its vapour 
tension at 10° C. is 1 mm. and at 20 0 C, 9 mm. The vapour 
density is 475 and its volatility at 20° C. is 75,000 mgm. per cu. m. 
(Miiller). 

The commercial product is yellow or brown. 

Bromoacetone is only slightly soluble in water, but very 
soluble in alcohol, ether, acetone and other organic solvents. 
It is not very stable, even in the pure state. 1 It polymerises in 
time, especially under the influence of light and heat, 2 though 
this process may be impeded by the addition of stabilising 
substances. During the war a small quantity of magnesium 
oxide was added to bromoacetone and this checked the 
polymerisation for several months (Meyer). 

Bromoacetone when distilled with steam partly passes over 
unaltered and partly decomposes to give an oily product containing 
little bromine, while the water is coloured brown. 

It combines readily with a variety of substances. With sodium 
bisulphite it forms a crystalline substance of the formula : 

CHgBr 
/OH 
I N S0 3 Na 
CH 3 

On passing well-dried ammonia into bromoacetone in ethereal 
solution, acicular crystals separate, probably due to the formation 
of an additive compound. 3 

By the action of hydrocyanic acid on bromoacetone 4 in the 
cold (i.e., at about o° C.) bromoacetone cyanohydrin is formed. 

1 Emmerling and Wagner, Ann., 1880, 204, 29. 

2 Giua and Rocciu, Atti accad. sci. Torino, 1932, 67, 409. 
8 Sokolovsky, Ber., 1876, 9, 1687. 

4 A. Chrzaszczevska and W. Sobieransky, loc. cit. 



BROMOMETHYL ETHYL KETONE 



This is a colourless liquid with a boiling point of 94-5° C. at a 
pressure of 5 mm. of mercury. Its specific gravity is 1-584 
at 13° C, and it is soluble in water, alcohol and ether. 

The bromine atom of bromoacetone is easily separated from 
the molecule and substituted by other atoms or radicles. Thus 
on treating bromoacetone with alcoholic potash, hydroxyacetone 
and potassium bromide are obtained ; with sodium iodide 
iodoacetone is formed, this being a substance with strongly 
lachrymatory properties, but of little importance as a war gas 
because of its high cost. 

Bromoacetone reacts with iron, but does not attack lead, so 
it is essential to store it in lead-lined containers. 

The animal fibres absorb more bromoacetone than do the 
vegetable fibres. The absorption capacity is fairly high and 
textiles are discoloured. It is found that textiles which are 
merely air-dried absorb more bromoacetone than those which 
have been completely freed from all water. 1 

For the purification of places contaminated with bromoacetone, 
spraying with a solution of 240 gm. " liver of sulphur " in 140 ml. 
of a soap solution diluted with 10 litres of water is recommended. 

The lower limit of irritation is 1 mgm. per cu. m. of air. The 
maximum concentration which a normal man can support for 
not more than 1 minute is 10 mgm. per cu. m. The mortality- 
product is 4,000 (Muller) or 32,000 (Prentiss). 

During the war of 1914-18 the French used a mixture of 
bromoacetone and chloroacetone (80 : 20) known as " Martonite." 
The reasons for the employment of this mixture are of a technical 
nature (see p. 151). 

3. Bromomethyl Ethyl Ketone. BrCH 2 — CO — C 2 H 5 (M.Wt. 151) 
This substance was employed in place of bromoacetone, whose 
production during the war period was impeded by the necessity 
of reserving acetone for the needs of the explosives industry. 

On the other hand, methyl ethyl ketone, the primary material 
in the preparation of this war gas, is easily obtainable even in 
wartime, for it is a by-product in the manufacture of acetone 
from pyroligneous acid. The monobromo- derivative of methyl 
ethyl ketone has similar aggressive properties to bromoacetone and 
was used by both the French and the Germans in the war of 1914-18 . 

Preparation 

This compound is prepared both in the laboratory and on the 
plant scale by a method similar to that already described for 

1 Alexejevsky, /. Prikl. Khimii., 1929, 1, 184. 



154 



HALOGEN ATED KETONES 



bromoacetone. That is, by brominating methyl ethyl ketone 
with sodium bromide in presence of sodium chlorate. In this 
preparation bromomethyl ethyl ketone is not the only product, 
a mixture with the isomeric methyl-a-bromoethyl ketone always 
being obtained. 1 

Physical and Chemical Properties 

Bromomethyl ethyl ketone is a colourless or pale yellowish 
liquid which boils at ordinary pressure at 145° to 146° C. with 
decomposition. Its specific gravity is 1-43. It is insoluble in 
water ; alteration on exposure to light is rapid. It is not 
decomposed by the action of water, and in general its chemical 
behaviour is very similar to that of bromoacetone. It is easily 
absorbed by active carbon. Places contaminated with bromo- 
methyl ethyl ketone can be decontaminated by spraying with a 
soapy solution of " liver of sulphur." 

Bromomethyl ethyl ketone is an irritant especially to the eyes. 
The minimum concentration capable of causing irritation of the 
eyes is i<6 mgm. per cu. m., according to Muller. The limit of 
insupportability is 11 mgm. per cu. m. of air (Fries), and the 
mortality-product is 6,000. 

(B) AROMATIC 

The halogenated ketones of the aromatic series may be prepared, 
like those of the aliphatic series, by the action of the halogens 
on the corresponding ketones. Some may be obtained by the 
Friedel and Craft synthesis, that is, by condensing an aromatic 
hydrocarbon with an aliphatic halogen acid in presence of 
anhydrous aluminium chloride. 

In the preparation of these war gases by direct halogenation it 
is necessary to follow the exact procedure given so as to introduce 
the halogen only into the side-chain, as compounds with a 
nuclear halogen atom have no lachrymatory properties. 

In order to ensure this, according to Graebe 2 and Staedel, 3 the 
halogenation should be carried out at the boiling point of the 
ketone, or, according to Gautier 4 and Hunnius, 5 by operating 
in presence of special solvents such as carbon disulphide, acetic 
acid or carbon tetrachloride, 6 which seem to have the function 
of directing the halogen atom into the side-chain. 

1 L. v. Reymenant, Bull. acad. ray. Belg., 1900, 724. 

2 Graebe, Ber., 1871, 4, 35. 

' Staedel, Ber., 1877, 10, 1830. 

1 Gautier, Ann. chim. phys., 1888, 14, 377. 

5 Hunnius, Ber., 1877, 10, 2006. 

» Ward, /. Chem. Soc, 1923, 123, 2207. 



CHLOROA CETOPHENONE 



155 



The aromatic halogenated ketones, unlike those of the aliphatic 
series, are quite stable compounds. Another difference is that 
the aromatic derivatives, although they contain a carbonyl 
group, form no additive compounds with bisulphite. 1 

Recently, some fluorinated members of this group have been 
prepared, such as fluoroacetophenone, 2 a brown liquid with a 
pungent odour, which boils at 98° C. at 8 mm. pressure. It is 
described as having lachrymatory properties, but the magnitude 
of these is not reported. 

An interesting fact concerning these compounds from the 
aggressive point of view is that the halogenated aromatic ketones 
have superior lachrymatory properties to the corresponding 
aliphatic compounds. Thus chloroacetophenone has a much 
more powerful lachrymatory action than the chloro- and even 
the bromo- derivative of acetone. This fact, besides having great 
advantages on the economic side — and being by no means 
negligible from the purely offensive point of view — indicates that 
it is not only the halogen to which the lachrymatory properties 
of these compounds is due, but also to the rest of the molecule to 
which the halogen is united. 

With regard to the biological properties, it has been found 
that several substances of this group, like a-chloroacetophenone 
and a-3'4 trichloroacetophenone, cause, 3 besides lachrymation, 
a painful sensation of itching when they penetrate the pores of 
the skin in the form of a vapour or a cloud. This action, as 
previously mentioned, is termed " orticant action." 

1. Chloroacetophenone. C 6 H 5 — CO — CH 2 C1 (M.Wt. 154 5) 

a-Chloroacetophenone — also termed ^-chloroacetophenone, 
phenacyl chloride or phenyl chloromethyl ketone — was prepared 
in 1871 by "^Graebe 4 by absorbing chlorine in acetophenone. 
Later, in 1884, Friedel and Craft 5 succeeded in obtaining it by 
the action of chloroacetyl chloride on benzene in presence of 
aluminium chloride : 

C 6 H 6 + C1CO— CH 2 C1 = C 6 H 6 — CO — CH 2 C1 + HC1. 

It may also be prepared by the action of diazomethane on 
benzoyl chloride in ethereal solution 6 : 

C 6 H 5 C0C1 + CH 2 N 2 = C 6 H 5 C0CH 2 C1 + N 2 , 

1 Nekrassov, op. ext. 

2 P. Ray, /. Indian Chem. Soc, 1935, 12, 93. 

3 M. Jastrzebsky and Suszko, Roczniki Chem., 1933, 13, 293. 

4 Graebe, Ber., 1871, 4, 35. 

6 Friedel and Craft, Ann. chim. phys., 1886, [6] 1, 507. 

6 Clibbens and Nierenstein, /. Chem. Soc, 1915, 107, 1492. 



156 



HALOGEN ATED KETONES 



or by the action of chloroacetyl chloride and aluminium trichloride 
on a solution of phenyl dichloroarsine in carbon disulphide. 1 

This compound, because of its lachrymatory properties was 
tested during the last war (1918) in Edgewood Arsenal and 
considered to be a useful and practicable war gas. 

It is designated in the Chemical Warfare Service of America 
as " CN." 

Laboratory Preparation 

It is prepared by the action of chlorine on acetophenone 
according to Korten and Scholl's method. 2 

20 gm. acetophenone and 100 gm. acetic acid are placed in a 
flask fitted with a stopper carrying two holes, through one of which 
passes a delivery tube for the chlorine and through the other an 
air-condenser. The mixture is agitated to facilitate the solution 
of the acetophenone and then the whole is weighed. A rapid 
stream of chlorine is passed through the solution, cooling 
externally if necessary until the necessary amount of chlorine 
has been absorbed. 

The product is allowed to stand at ordinary temperature until 
the liquid becomes colourless. It is then poured into ice-water ; the 
chloroacetophenone separates as an oily liquid which rapidly 
solidifies. The crystals are separated and crystallised from 
dilute alcohol. 

Industrial Manufacture 

The manufacture of chloroacetophenone commencing with 
acetic acid comprises the following steps : 

(1) Preparation of Monochloroacetic acid : 

CH3COOH + Cl 2 = CH 2 ClCOOH + HC1. 

(2) Chlorination of Monochloroacetic Acid to obtain chloroacetyl 
chloride : 

4CH 2 C1C00H + S 2 C1 2 + 30s, = 4CH 2 C1— C0C1 + 2S0 2 + 4HCI. 

This chlorination may be carried out either by means of chlorine 
and sulphur monochloride or by the action of phosphorus 
trichloride. 

(3) Condensation of Chloroacetyl Chloride with Benzene : 

C 6 H 6 + CH 2 C1— C0C1 = C 6 H 6 CO— CH 2 C1+HC1. 
Operating Details. The glacial acetic acid is placed in a lead- 

1 Gibson and coll., Rec. trav. chim., 1930, 49, 1006. 
a Korten and Scholl, Ber., 1901, 34, 1902. 



CHLOROACETOPHENONE : PROPERTIES 157 



lined vessel fitted with a thermometer and a fractionating column 
connected with an absorption tower, which is filled with coke 
and serves to absorb the hydrochloric acid. The vessel is heated 
to about 98 0 C, while the calculated quantity of dry chlorine gas 
is slowly passed in. 

Monochloroacetic acid is thus obtained and this is transferred 
without further purification to another similar vessel. Sulphur 
monochloride is added, and chlorine is introduced, while heating 
to 45° C, to complete the chlorination. The chlorinated product 
is then transferred to a third vessel in which fractional distillation 
separates the chloroacetyl chloride from the other products 
(sulphur chloride, excess monochloroacetic acid, etc.). 

The calculated quantities of benzene and aluminium chloride 
are placed in an enamelled vessel and maintained at 25° C. 
The chloroacetyl chloride is then added in small quantities 
while the mixture is agitated. At the end of this addition, the 
mass is warmed to 60° to yo° C. for 2 hours and then poured into 
cold water. The layer containing the chloroacetophenone is 
freed from benzene by distillation and the chloroacetophenone 
finally purified by steam distillation. 

Physical and Chemical Properties 

Chloroacetophenone forms colourless or slightly yellowish 
crystals which melt at 58° to 59° C. (Staedel). 

It boils at ordinary pressure at 244° to 245° C. and may be 
distilled without any decomposition. At 14 mm. mercury 
pressure it boils at 139° to 141° C. Its specific gravity at various 
temperatures is as follows : 



The vapour tension of chloroacetophenone at ordinary tempera- 
tures is very low. It is given as a function of temperature in the 
following table : 



TEMPERATURE 



S.G. 



15 
25 
55 



o 



1-334 
1-324 
i-3i3 
1-263 



TEMPERATURE 
°C. 



VAPOUR TENSION 
MM. MERCURY 



15 
25 

35 
55 



o 



0-0017 
0-0078 
0-0198 
0-0473 
0-158 



158 



HALOGEN ATED KETONES 



The volatility is 30 mgm. per cu. m. of air at o° C, and 105 
mgm. per cu. m. at 20° C. 

The specific heat of chloroacetophenone is 0*264 calorie and 
the latent heat of evaporation 89 calories. 

Chloroacetophenone is soluble in alcohol, benzene (40% by 
weight), ether and carbon disulphide, 1 as well as in many of the 
other war gases. For instance, phosgene dissolves 9-5% by 
weight, and cyanogen chloride 63% by weight. It is, however, 
very slightly soluble in titanium tetrachloride, silicon tetrachloride 
or water (1 gm. in 1,000 ml.). 

The solubility of chloroacetophenone in the readily volatile 
solvents is utilised in diffusing it in air. For this purpose benzene 
is the best solvent, carbon tetrachloride also being occasionally 
employed. When a solution in one of these solvents is sprayed 
into the air the solvent evaporates rapidly, leaving the chloro- 
acetophenone dispersed in a state of fine subdivision. 

Chloroacetophenone is quite stable. It is not hydrolysed by 
water even on boiling and it is unaffected by humidity. It is 
completely decomposed by 60% oleum. Hot aqueous solutions of 
sodium carbonate convert it into hydroxymethyl phenyl ketone 
of the formula (Graebe), C 6 H 5 — CO — CH 2 OH, which forms 
crystals melting at 86° C. and boiling at 118° C. at 11 mm. 
mercury pressure. It is soluble in alcohol, ether and chloroform. 

Chloroacetophenone is oxidised in benzene solution by such 
oxidising agents as chromic acid or potassium permanganate to 
benzoic acid. 

By adding it in small quantities to a mixture of fuming nitric 
acid and sulphuric acid, shaking after each addition, it is converted 
into benzoic acid and m-nitro-oc-chloroacetophenone 2 : 

COCH 2 Cl 
/\ 



\/N0 8 

This forms crystals melting at 100-5° to 102° C. 

By bubbling gaseous chlorine through chloroacetophenone 
in presence of aluminium iodide or chloride, aa-dichloroaceto- 
phenone 3 is formed : 

C 6 H 5 COCH a Cl + Cl 8 = C 6 H 5 C0CHC1 2 + HC1. 
This is obtained as crystals melting at 20° to 21-5° C. Its density 
1 Staedel, Ber., 1877, 10, 1830. 

4 Barkenbus and Clements, /. Am. Chem. Soc, 1934, 56> 1369- 
8 H. Gautier, Ann. chim.phys., 1888, [6] 14, 345-385. 



CHLOROACETOPHENONE : PROPERTIES 159 

is 1-34 at 15 0 C, and it boils at ordinary pressure at 247° C. with 
decomposition. At 25 mm. pressure it distils unaltered at 143° C. 
It has inferior lachrymatory properties to chloroacetophenone. 

With more vigorous chlorination, at a temperature of 200 0 C. 
aided by sunlight, aaa-trichloroacetophenone 1 is formed : 

C 6 H 6 C0CH 2 C1 + 2 C1 2 = C 6 H 5 C0CC1 3 + 2HCI. 

This is a liquid boiling at 145° C. at 25 mm. pressure and having 
a density of 1-425 at 16° C. 

Chloroacetophenone reacts with sodium iodide in solution in 
aqueous alcohol, forming a-iodoacetophenone 2 : 

C 6 H 6 C0CH 2 C1 + Nal = C 6 H 5 COCH 2 I + NaCl. 

This is a crystalline substance melting at 29-5° to 30° C, which 
boils at 170 0 C. at 30 mm. pressure and is insoluble in water, but 
soluble in alcohol, ether and benzene. 

With hydriodic acid or, better, by boiling with an acetic acid 
solution of potassium iodide, chloroacetophenone separates 
iodine and forms acetophenone 3 : 

C 6 H 8 C0CH 2 C1 + 2HI = C s H 8 COCH 3 + HC1 + I 2 . 

Alcoholic ammonia converts chloroacetophenone in the cold to 
a-aminoacetophenone 4 : 

C 6 H 6 C0CH 2 C1 + HNH 2 = C 6 H 5 COCH 2 NH 2 + HC1, 

which is partly converted into iso-indole. 
With aniline, phenacyl aniline is formed 5 : 

C 6 H 5 C0CH 2 C1 + NH 2 C 6 H 5 = C 6 H 6 COCH 2 .NHC 6 H 6 + HC1. 

Urotropine forms an additive product of the formula 6 

C 6 H 5 COCH 2 [N 4 (CH 2 ) 6 ]Cl. 

which forms crystals melting at 145 0 C. 

Chloroacetophenone dissolved in alcohol reacts at 60° C. with 
an alcoholic solution of sodium sulphide to form phenacyl 
sulphide, as follows 7 : 

2 C 6 H 6 C0CH 2 C1 + Na 2 S = (C 6 H 8 COCH 8 ) 2 S + 2NaCl. 

This is a colourless crystalline compound, melting at 76-5° to 
77-2° C, odourless, insoluble in water, but soluble in alcohol, 

1 H. Gautier, Ann. chim. phys., 1888, [6] 14, 396. 

2 A. Collet, Compt. rend., 1899, 128, 312 ; Matheson, /. Chem. Soc, 1931, 2515. 

3 Pancenko, loc. cit. 

« W. Staedkl and coll., Bet., 1876, 9, 563. 

6 Mohlau, Ber., 1882, 15, 2466; Matheson, /. Chem. Soc., 1931, 2514. 

6 Mannich and Hahn, Ber., 1911, 44, 1542. 

7 Tafel, Ber., 1890, 23, 3474 ; A. Chrzaszczevska and Chvalinsky, Roczniki 
Chem., 1927, 7, 67. 



i6o 



HALOGEN ATED KETONES 



ether and acetic acid. On heating to 100° C. it decomposes, 
forming hydrogen sulphide, acetophenone and products whose 
nature has not yet been defined. 

By boiling an alcoholic solution of chloroacetophenone with 
an aqueous solution of sodium thiosulphate, the sodium salt of 
phenacyl thiosulphuric acid is formed : 

C 6 H 5 C0CH 2 C1 + Na 2 S 2 0 3 = NaCl + C 6 H 5 COCH 2 .S 2 0 3 Na. 

On refluxing equimolecular amounts of chloroacetophenone 
and potassium thiocyanate together, needle-shaped crystals are 
formed of the following formula : 

C 6 H 5 COCH 2 SCN. 

which melt at 72° to 73 0 C. and are soluble in alcohol, ether and 
chloroform. 1 

1 mol. chloroacetophenone reacts with 3 mols. hydroxylamine 
hydrochloride in dilute methanol solution at ordinary tempera- 
tures, with formation of oc-chloroacetophenone oxime, of the 
formula 2 : 

C 6 H 5 — C— C H 2 C1 
HO-N 

This forms crystals melting at 88-5° to 89 0 C. whose vapours have 
a powerful lachrymatory action. This substance causes persistent 
and strong irritation when applied to the skin in the solid state 
or in solution. 

Chloroacetophenone, on treatment in the cold with sodium 
phenate in aqueous or alcoholic solutions, reacts as follows 3 : 

C 6 H 5 C0CH 2 C1 + NaOC 6 H 5 = C 8 H 5 COCH 2 .OC 6 H 5 + NaCl. 

Chloroacetophenone does not attack iron containers. It is 
resistant to heat and insensitive to detonation, so that it can be 
loaded into projectiles without fear of its suffering change. 

It was used, melted with magnesium oxide and mixed with 
nitrocellulose, for the preparation of irritant candles. 4 

Graebe noted that the vapours of chloroacetophenone irritated 
the eyes, and the Americans (Fries) have found that a con- 
centration of 0-3 mgm. per cu. m. of air is sufficient to provoke 
lachrymation. According to Miiller, 5 the lachrymatory action 
commences at a concentration of 0-5 mgm. per cu. m., while it 

1 Dyckerhof, Ber., 1877, 10, 119. 

2 Korten and Scholl, Ber., 1901, 34, 1901. 
s Lellmann, Ber., 1890, 23, 172. 

4 Federal Laboratory, U.S. Pat. 1,864,754. 

6 Muller, Militar-Wochenblatt., 1931, 116, 754. 



BROMOACETOPHENONE 



161 



irritates the nose at i mgm. per cu. m. At a concentration of 
2 mgm. per cu. m. it causes irritation of the skin of the face. 

Besides its lachrymatory action, this substance has an 
" orticant " action on the skin if diffused in the air in sufficient 
concentration (100 mg. per cu. m. according to Miiller). 

The limit of insupportability is 4-5 mgm. per cu. m. The 
mortality-product is 4,000 according to Miiller and 8,500 according 
to American experiments (Prentiss). 

2. Bromoacetophenone. C 6 H 5 — CO — CH jBr (M.Wt. 199) 

Bromoacetophenone was obtained by Emmerling and Engler 1 
by the reaction of bromine on acetophenone. 

C 6 H 5 CO-CH 3 + Br 2 = C 6 H 5 -CO-CH 2 Br + HBr. 
Preparation 

In the laboratory it is usually prepared by Mohlau's 2 modifica- 
tion of Emmerling' s original method, that is, by the action of 
bromine on acetophenone. 

25 gm. acetophenone and 125 gm. acetic acid are placed in a 
flask through whose stopper passes a reflux condenser, a tap-funnel 
and a delivery-tube for carbon dioxide. While agitating the 
contents of the flask, 30 gm. bromine 3 are added little by little 
from the tap-funnel, meanwhile passing a current of carbon 
dioxide through the liquid to remove the hydrobromic acid 
formed in the reaction. When all the bromine has been added, 
the current of carbon dioxide is continued for 5-10 minutes and 
then the whole allowed to stand for about 1 hour before heating 
on the water-bath to remove the carbon dioxide completely. 
When the liquid in the flask is colourless it is poured into much 
water. The bromoacetophenone separates for the most part as a 
yellow oil which forms a crystalline mass on cooling. The crystals 
are collected and purified by alcohol. 

Physical and Chemical Properties 

Bromoacetophenone forms white rhombic prisms which become 
greenish on exposure to light, owing to incipient decomposition. 
It melts at 50° C. and boils at ordinary pressure at 260° C. with 
decomposition, and at 12 mm. mercury pressure at 133° to 135° C. 
with partial decomposition. It is insoluble in water, but soluble 
in the common organic solvents (alcohol, ether, benzene, etc). 

Bromoacetophenone is not decomposed by water even on 

1 Emmerling and Engler, Ber., 1871, 4, 147. 

* MShlau, Ber., 1882, 15, 2465. 

* Ward, /. Chem. Soc, 1923, 123, 2207. 

WAR OASES. 6 



l62 



HALOGEN ATED KETONES 



boiling. With potassium permanganate it reacts to form benzoic 
acid. 1 With cold fuming nitric acid it gives bromotrinitro- 
acetophenone. 

Treated in the cold with alcoholic ammonia, it forms iso-indole. 
The reaction with aniline is more vigorous than in the case of 
chloroacetophenone. 2 

Bromoacetophenone 3 in alcoholic solution when treated with 
an alcoholic solution of sodium sulphide reacts vigorously, 
evolving hydrogen sulphide and forming a crystalline mass of 
phenacyl sulphide (see p. 159). 

SfCgl^COCH^. 

On treatment in the cold with sodium phenate in aqueous or 
alcoholic solution, bromoacetophenone reacts according to the 
equation 4 : 

C 6 H 5 COCH 2 Br + C 6 H 5 ONa = NaBr + C 6 H 5 COCH 2 .OC 6 H 6 . 

It combines with hexamethylene tetramine to form an additive 
product of the formula : 

C„H 5 — CO— CH 2 [N 4 (CH 2 ) 6 ]Br, 

which forms crystals melting at 165° C. 5 

The lachrymatory power of bromoacetophenone is less than 
that of chloroacetophenone. 

1 Hunnius and Engler, Ber., 1878, 11, 932. 

2 Matheson and coll., /. Chem. Soc, 1931, 2514. 
8 Tafel and Mauritz, Ber., 1890, 23, 3474. 

* R. Mohlau, Ber., 1882, 15, 2498. 
6 Mannich, Ber., 1911, 44, 1545. 



CHAPTER XII 



HALOGENATED NITRO- COMPOUNDS 

The presence in a molecule of a nitrogen atom united by a 
double link to an oxygen almost always involves a certain degree 
of toxicity. Moreover, this toxicity is increased and lachrymatory 
action is added if halogen atoms are also present. 

During the last war much interest was taken in the trihalogen 
derivatives of nitromethane as war gases : 

CC1 3 N0 2 Trichloronitromethane, or chloropicrin. 
CBr 3 N0 2 Tribromonitromethane, or bromopicrin. 

Since the war, research on the halogenated nitro- compounds 
has been continued, especially on the corresponding compounds 
of the higher homologues of methane. The following results have 
been obtained : 

(1) Symmetrical dichlorotetranitro ethane, 1 obtained by the 
action of chlorine on the potassium salt of symmetrical tetranitro 
ethane : 

CK(NO a ) = CCl(NO a)s +zKC1 

CK(N0 2 ) 2 2 CC1(N0 2 ) 2 

forms crystals melting at 105° C. a 

(2) Symmetrical tetrachlorodinitro ethane, obtained by the 
action of fuming nitric acid on tetrachloro ethylene 3 : 

CC1 2 -> CCl-sNO, 

to, CC1 2 N0 2 

forms crystals melting at 142° to 143 0 C. 

(3) a a /? Tribromo a /3 dinitro ethane* obtained by the action 
of oxides of nitrogen on tribromo ethylene in a closed tube 
at 40 0 C. 

CBr 2 -> CBr 2 N0 2 
CHBr CHBrN0 2 
forms colourless crystals melting at 133° to 134° C. 

1 Hunter, /. Chem. Soc., 1924, 125, 1480. 

2 Burrows, /. Chem. Soc, 1932, 1360. 

3 Biltz, Ber., 1902, 35, 1529 ; Argo and James, /. Phys. Chem., 1919, 23, 578. 

4 Burrows, /. Chem. Soc., 1932, 1357. 

163 6—2 



164 HALOGEN ATED NITRO- COMPOUNDS 

These compounds all have lachrymatory power, especially 
tetrachloro dinitro ethane, which is much more powerful in this 
respect than chloropicrin. 

Some of the halogenated derivatives of unsaturated nitro- 
compounds have also been examined, e.g., chloronitro ethylene 
(CH 2 = CC1N0 2 ) and various of its homologues. 1 These 
compounds, though having powerful lachrymatory properties, 
cannot be considered for use as war gases for owing to the 
presence of the unsaturated linkage in their molecules they tend 
to polymerise forming substances without lachrymatory properties. 

Recently other substances having a certain amount of interest 
in war gas chemistry have been prepared : 

(1) Trifluoronitroso methane, 2 obtained by the action of fluorine 
on silver cyanide in the presence of silver nitrate, is a bright blue 
gas, fairly stable chemically. It melts at — 150 0 C, boils at 
— 80° C. and has an unpleasant odour. 

(2) Trichloronitroso methane, 3 obtained by the action of nitric 
acid on the sodium salt of trichloromethyl sulphinic acid, is a 
liquid boiling at 5° C. at 70 mm. pressure. 

Both these substances have an irritant action. 

1. Trichloro Nitroso Methane. CCl 3 NO (M.Wt. 148) 

Trichloronitroso methane has been prepared recently by 
Prandtl and Sennewald 4 by the action of nitric acid on the sodium 
salt of trichloromethyl sulphinic acid : 



A very violent reaction takes place and the yield of trichloro 
nitroso methane is low. This compound is more conveniently 
obtained by the action of an aqueous solution of sodium trichloro 
methyl sulphinate, potassium nitrate and sodium nitrite on 
sulphuric acid. 6 

Laboratory Preparation 

250 ml. 20% sulphuric acid are placed in a round-bottomed 
flask fitted with a tap-funnel and a well-cooled coil-condenser. 
The flask is heated to 70 0 C. and a cold solution of 94 gm. sodium 
trichloromethyl sulphinate, 50 gm. potassium nitrate and 25 gm. 
sodium nitrate in 300 ml. water is dropped in from the tap-funnel, 

1 Wilkendorf, Ber., 1924, 57, 308 ; Schmidt and Rutz, Bet., 1928, 61, 2142. 

2 O. Ruff, Ber., 1936, 69, 598, 684. 

3 Prandtl and Sennewald, Ber., 1929, 62, 1754. 

4 Prandtl and Sennewald, loc. cit. 

6 Prandtl and Dollfus, Ber., 1932, 65, 756. 



so. 




TRICHLORONITROSO METHANE : CHLOROPICRIN 165 



regulating the rate of addition so that the internal temperature 
is maintained at 70° C. by the heat of reaction. The contents of 
the flask suddenly turn blue and the trichloronitroso methane 
commences to distil, collecting in the receiver, which is cooled 
by ice, as a blue liquid. The yield is 75-80%. 

Physical and Chemical Properties 

It is a dark blue liquid which when boiled at ordinary pressures 
partially decomposes. It boils undecomposed at 5 0 C. at a 
pressure of 70 mm. Its specific gravity is 1-5 at 20° C. 

It is insoluble in water, but dissolves in the common organic 
solvents. On storing at ordinary temperature in a sealed glass 
container, it decomposes in 2-3 months with formation of nitrosyl 
chloride, oxides of nitrogen and chloropicrin. It is much more 
stable in solution. 

It reacts slowly with aqueous alkaline solutions and rapidly in 
presence of ether. 

Oxygen and oxidising agents transform it into various 
compounds, among which chloropicrin has been identified. On 
reduction with hydrogen sulphide, dichloro formoxime (see p. 77) 
is formed : 

CCI3NO + H 2 S Cl 2 = C = NOH + S + HC1. 

The vapour of trichloronitroso methane strongly attacks 
rubber. 

Both in the liquid and the vapour states it has a disagreeable 
odour ; irritation is caused to the eyes and to the respiratory 
tract, lachrymation and coughing being produced. 

2. Chloropicrin. CC1 3 N0 2 (M.Wt. 164-5) 

Chloropicrin, or trichloronitromethane, was prepared in 1848 
by Stenhouse. 1 In the war of 1914-18 it was largely employed 
as a war gas, more particularly as it combined a simple and 
economic manufacture with many of the characteristic desiderata 
of a war gas. 

It was first employed by the Russians in 1916 in hand-grenades, 
dissolved in sulphuryl chloride (50%). 

Chloropicrin is also known as " Klop " (Germany), " Aquinite " 
(France), and "PS" (America). 

It has found application as an insecticide and fungicide 2 and 
has been used for eradicating rats from ships. 3 

1 Stenhouse, Ann., 1848, 66, 241. 

* G. Bertrand, Compt. rend., 1919, 168, 742 ; Chim. et Ind., 1937, 37 > 4 r 9- 

* A. Piutti, Rend, accad. sci. Napoli, 1918, 26, para. iii. 



166 HALOGEN ATED NITRO- COMPOUNDS 



Preparation 

Various methods have been proposed for the preparation of 
chloropicrin. For example : 

(1) By the action of picric acid on calcium hypochlorite. 1 

(2) By the action of chlorine on nitromethane or mercury 
fulminate. 2 

(3) By the action of nitric acid on certain chlorinated organic 
compounds, as chloroform, 3 chloral, 4 trichloroethylene, 5 etc. 

(4) By the action of a mixture of nitric and hydrochloric acids 
on the by-products of acetone manufacture. 6 

The method which was most used during the war of 1914-18 
was that of the action of picric acid on calcium hypochlorite. 
This method was not very suitable in practice, for it required 
as raw material a substance not easily spared during the war, 
when it was needed for the explosive industry. The other 
methods of production referred to above have been studied since 
the war, showing the interest of chemists in working out a method 
which does not require the use of a raw material of limited 
accessibility. 

Laboratory Preparation 

Chloropicrin may be prepared in the laboratory by the method 
proposed by Hoffmann. 7 

550 gm. chloride of lime made into a paste with about 1 litre 
water are placed in a 5-litre flask. A paste of sodium picrate, 
made by mixing 50 gm. picric acid with 10 gm. sodium hydroxide 
and 250 ml. water, is added with continuous stirring. The flask 
is then fitted with a stopper carrying a long condenser and the 
contents steam-distilled until no more oily droplets come over. 

The reaction takes place very rapidly and is completed in 
about £ hour. The oily distillate is separated from the water in 
a separatory funnel, dried over calcium chloride and redistilled. 

Yield 70% of the theoretical. 

Industrial Manufacture 

The various methods used during the war for the manufacture 
of chloropicrin do not differ greatly from Hoffmann's method 
given above. 

1 Stenhouse, Ann., 1848, 66, 241 ; Hoffmann, Ann., 1866, 139, 111. 

2 Kekule, Ann., 1857, 101, 204. 
s Mills, Ann., 1871, 160, 117. 

* Kekule, Ann., 1857, 101, 212 ; N. Danaila and Soare, Bui, chim. soc. 
romdnd stiinte, 1932, 35, 53. 

6 R. Burrows and Hunter, /. Chem. Soc, 1932, 1357. 

6 G. Sanna, Rend. sent. fac. sci. Cagliari, 1933, 2, 87. 

7 Hoffmann, Ann., 1866, 139, m. 



CHLOROPICRIN : MANUFACTURE 167 



In the German plants a paste of chloride of lime and water 
was treated in large vessels of 2-3 m. diameter and 4-5 m. depth 
with picric acid added in small amounts at a time, the temperature 
being maintained at about 30° C. The mixture was then distilled 
in a current of steam, the distillate being collected in large 
receivers where the chloropicrin was separated from water. 

The Americans preferred to use calcium picrate instead of the 
sparingly soluble picric acid, proceeding in the following 
manner 1 : 

A paste of chloride of lime was first prepared and pumped 
into a vertical vessel of enamelled iron where it was mixed with 
calcium picrate prepared previously by mixing picric acid with 
water and an excess of lime. The mixture was allowed to 
react at ordinary temperatures for about 2 hours and then a 
current of steam was introduced at the bottom of the vessel. In 
these conditions the rise in temperature accelerated the reaction 
and at 85° C. the chloropicrin began to distil. Distillation was 
continued until no more chloropicrin came over. 

According to a patent by Orton and Pope, 2 chloropicrin may 
also be obtained by the direct action of chlorine on picric acid, 
or other nitro-derivative of phenol or of naphthol : 

C 6 H 2 (N0 2 ) 3 OH + nCl 2 + 5 H 2 0 = 3 CC1 3 N0 2 + 13HCI + 3 C0 2 . 

The reaction is carried out in alkaline solution (sodium or 
potassium hydroxide, or a mixture of the corresponding 
carbonates) so as to dissolve the nitro-compound and to neutralise 
the hydrochloric acid which otherwise impedes the chlorination 
of the picric acid. The reaction takes place very readily at a low 
temperature (between o and 5° C). 

Recently a new method of preparation of chloropicrin has been 
worked out in Rumania. 3 This uses petroleum as raw material. 
The principal stages of the preparation of chloropicrin by this 
process are as follows : 

(a) Nitration of hydrocarbons present in the petroleum. 

(b) Chlorination of the nitro-compounds obtained with 
chloride of lime. 

(c) Distillation of the chloropicrin in a current of steam. 

Physical and Chemical Properties 

Chloropicrin in the pure state is a slightly oily, colourless, 
refractive liquid with a characteristic odour. The crude product 
is yellow due to impurities. 

1 Trumbull and coll., /. Ind. Eng. Chem., 1920, 12, 1068. 

2 Orton and Pope, Brit. Pat., 142,878/1918. 

3 Radulescu and Secareanu, Antigaz, 1927, No. 6, 3. 



168 HALOGEN ATED NITRO- COMPOUNDS 



It boils at 112° C. at 760 mm. pressure and at 49° C. at 40 mm. 
of mercury. 1 It solidifies at — 69-2° C. 

It may be distilled in a current of steam without decomposition. 

The specific gravity of chloropicrin between 0° and 50° C. is 
as follows : 



TEMPERATURE (° C.) 


S.G. 


TEMPERATURE (° C.) 


S.G. 


O 


1-6930 


30 


1-6400 


10 


1-6755 


40 


1-6219 


20 


1-6579 


50 


1-6037 



The coefficient of expansion at various temperatures is as 
follows : 

At 0° C. . 0-00I02 At 30° C. . 0-00106 



At 10° C. 



0-00103 



At 50° C. . o-oono 



Its specific heat between 15° and 35° C. is 0-235 ; its latent 
heat of evaporation is 59 calories. Its vapour density compared 
with that of air is 5-69. The vapour tension of chloropicrin at 
any temperature t may be calculated empirically 2 by employing 
the formula (see p. 5) : 

2045-2 



log p = 8-2424 — 



273 + t 



In the following table the values of the vapour tension are 
reported together with the corresponding volatilities at various 
temperatures 3 : 



TEMPERATURE 
"C. 


VAPOUR TENSION 
MM. HG. 


VOLATILITY 
MGM. /LITRE 


0 


5-9i 


57-4 


10 


10-87 


104 


15 


14-12 


136 


20 


16-91 


184 


25 


23-81 




30 


30-50 


295 


35 


40-14 




50 


807 


748 



1 Cossa, Gazz. chim. ltd., 1872, 2, 181. 

* Baxter and Bezzenberger, /. Am. Chem. Soc, 1920, 42, 1386. 
3 Krczil, Untersuchung und Bewertung Techn. Adsorptionsstoffe, Leipzig, 
1931, 422. 



CHLOROPICRIN : PHYSICAL PROPERTIES 169 



The solubility of chloropicrin in water is very low ; according 
to Thompson and Black 1 100 gm. water dissolve the following 
amounts of chloropicrin : 

° C. GM. 

O 0-22 
IO 0-I9 
20 0-I7 

30 0-15 
40 0-14 
75 o-ii 

The solubility of water in chloropicrin is also very low : 

° C. GM. IN IOO GM. WATER 
32 0-I003 
36 0-II85 
48 0-I647 

55 0-2265 

These low mutual solubilities facilitate their separation in the 
preparation and render drying of the chloropicrin unnecessary, 
unless it is to be employed for some special purpose, as, for 
example, in " NC " mixture (80% chloropicrin and 20% stannic 
chloride). 

Chloropicrin dissolves easily in benzine, carbon disulphide and 
ethyl alcohol (1 part dissolves 3-7 parts chloropicrin at water-bath 
temperature). In ether it is, however, relatively sparingly 
soluble. (At ii° C, 5 volumes ether dissolve 1*5 volumes 
chloropicrin — Cossa.) 

Chloropicrin is a fairly stable compound. It is not hydrolysed 
by water 2 and not attacked by mineral acids like hydrochloric, 
nitric and sulphuric, either cold or hot. Only 20% oleum 
decomposes it with formation of phosgene and nitrosyl sulphuric 
acid. 3 

On heating to 112° C, according to some authorities (Stenhouse, 
Cossa, etc.), it distils unchanged, while, according to others,* 
when maintained gently boiling it partially decomposes into 
phosgene and nitrosyl chloride : 

CCl 3 NO a -> COCl 2 + NOC1. 

The presence of some metals like copper, tin, zinc, aluminium, 
iron and lead only slightly influences the velocity of decomposition 
even at boiling point. 5 

1 T. Thompson and Black, /. Ind. Eng. Chem., 1920, 12, 1066. 

8 P. Ron a, Z. ges. expt. med., 1921, 13, 16. 

• Secareanu, Bull. soc. chim., 1927. 41, 630. 

4 I. A. Garden and F. Fox, /. Chem. Soc, 1919, 115, 1188. 

6 A. Petrov and coll., /. Prikl. Khim., 1929, 2, 629. 



HALOGEN ATED NITRO- COMPOUNDS 



By passing chloropicrin in the vapour state through a red-hot 
tube of quartz or porcelain, it decomposes with formation of 
chlorine and nitric oxide, while hexachloroethane deposits on the 
cold part of the tube. 1 

According to the researches of Piutti, 2 chloropicrin decomposes 
as follows when exposed to ultra-violet rays : 

CC1 3 N0 2 -> NOC1 + COCl 2 -+ CO + Cl 2 . 

A similar decomposition takes place when an aqueous solution 
of chloropicrin is shaken with wood-charcoal, previously activated 
by treatment with sodium hydroxide and heating to 450 0 C. 8 

Reducing agents convert it into various products according 
to the nature of the reducant and the conditions of reduction. 
Thus Raschig 4 obtained cyanogen chloride with stannous 
chloride and hydrochloric acid ; Geisse, 6 with iron filings and 
acetic acid, obtained methylamine : 

CC1 3 N0 2 + 6H 2 = CH 3 NH 2 + 3HCI + zH 2 0. 

Frankland 6 observed that the best results are obtained in this 
reaction by adding the chloropicrin in small portions to a mixture 
of iron filings and acidified water. 

On treatment of chloropicrin with an aqueous solution of 
sodium or potassium hydroxide there is no reaction, but if 
alcoholic soda or potash is employed, a gradual decomposition 
takes place and after a time crystals of potassium chloride 
separate. 

Aqueous ammonia does not react with chloropicrin. However, 
if the latter is saturated with ammonia gas, or even brought into 
reaction with an alcoholic solution of ammonia, ammonium 
chloride and nitrate are formed (Stenhouse). According to 
Hoffmann, 7 on heating chloropicrin in an autoclave to 100 °C. 
with an alcoholic solution of ammonia, guanidine is formed 
according to the following equation : 

/NH 2 

CC1 3 N0 2 + 3 NH, = NH=C< + 3 HC1 + HNO» 

NH 2 

By the action of alcoholic sodium sulphide 8 on chloropicrin 
also dissolved in alcohol, a violent reaction takes place, heat is 

1 Stenhouse, Ann., 1848, 66, 244. 

2 A. Piutti and Mazza, Atti accad. set. Napoli, 1926, 32, 97. 

3 Alexejevsky, /. Obscei Khim., Ser. A., 1932, 2, 341. 

4 Raschig, Ber., 1885, 18, 3326. 
6 Geisse, Ann., 1859, 109, 284. 

6 Frankland, /. Chem. Soc, 1919, 115, 159. 

7 Hoffmann, Ber., 1868, 1, 145. 

8 Kretov and Melnikov, /. Obscei Khim., Ser. A., 1932, 2, 202. 



CHLOROPICRIN : CHEMICAL PROPERTIES 171 



developed and a tarry material separates. According to the 
conditions of the reaction there are formed carbon monoxide, 
nitric oxide, nitrogen, carbon dioxide, sodium chloride, sulphur, 
etc. 

2 CC1 3 N0 2 4- 3 Naj-S = 3S + N 2 + 2 C0 2 + 6NaCl 
2 CC1 3 N0 2 + 3 NaaS = 3S + 2CO + 2NO + 6 NaCl 

Chloropicrin reacts with sodium or potassium sulphite, forming 
the corresponding salt of nitromethane disulphonic acid 1 : 

CC1 3 N0 2 + 3Na 2 S0 3 + H 2 0 = CHN0 2 (S0 3 Na) 2 + 3NaCl+NaHS0 4 

This reaction must be brought about by • heating to 90° to 
100° C, and takes place very rapidly in alcoholic as well as 
aqueous solution. The product of the reaction, sodium nitro 
methane disulphonate, forms small spheroidal plates, soluble 
with difficulty in cold water but easily in hot water. According 
to Rathke, 2 if the reactants are heated excessively a salt is 
obtained which no longer contains the N0 2 — group and to 
which he attributes the formula CH(S0 3 Na) 3 . 

By the action of potassium bromide on chloropicrin, tribromo 
nitromethane or bromopicrin is obtained, together with carbon 
tetrabromide, nitromethane, etc. 

Potassium iodide reacts with chloropicrin, giving no triiodo 
nitromethane, but completely decomposing the molecule with 
formation of carbon tetraiodide, as follows 3 : 

CC1 3 N0 2 + 4KI = CI 4 + 3KCI + KN0 2 . 

Even in the presence of insufficient potassium iodide, no 
triiodo nitromethane is formed. 

Sodium cyanide in aqueous-alcoholic solution reacts energetically 
with chloropicrin to form various compounds : sodium chloride, 
nitrite, carbonate and oxalate, cyanogen chloride, etc. 4 

Chloropicrin reacts even at ordinary temperature with sodium 
ethylate, forming sodium nitrite and chloride and the tetra ethyl 
ester of orthocarbonic acid 5 : 

CClsNO, + 4C 2 H 8 ONa = C(OC 2 H 5 ) 4 + 3 NaCl + NaN0 2 . 

Sodium methylate reacts similarly. 6 This reaction also 
takes place when sodium reacts with an alcoholic solution of 
chloropicrin. 7 

1 Rathke, Ann., 1872, 161, 153 ; Backer, Rec. trav. chim., 1930, 49, 1107. 

1 Rathke, Ann., 1873, 167, 219. 

s G. D. Ssychev, /. Khim. Promiscl., 1930, 7, 1168. 

» Bassett, Jahresb. fortschr. Chem., 1866, 495 ; Nekrassov, op. cit. 

6 H. Bassett, Ann., 1864, 132, 54 ; Rose, Ann, 1880, 205, 249. 

6 H. Hartel, Ber., 1927, 60, 1841. 

' Alexejevsky, /. Khim. Promiscl., 1931, 8, 50. 



HALOGEN ATED NITRO- COMPOUNDS 



Chloropicrin reacts with mercaptans at the ordinary tempera- 
ture, forming hydrochloric acid and the ester of orthonitro 
trithioformic acid : 

3R.SH + CC1 3 N0 2 = (R.S)s— C— N0 2 + 3HCI. 

The researches of Ray and Das 1 show that on heating, the 
reaction takes place very rapidly and nitrous gases are evolved : 

2(R.S) 3 — C— N0 2 -> (R.S) 3 — C— 0— C— (R.S) 3 + N 2 0 3 . 

Later researches by Nekrassov, 2 however, have demonstrated 
that chloropicrin in these conditions behaves as an oxidising 
agent on the mercaptan, so that a disulphide of the formula 
R.S.S.R and also carbon monoxide and nitrogen are formed. 

2(R.S) 3 — C— N0 2 3R— S— S— R + 2C0 2 + N 2 . 

In this reaction between chloropicrin and mercaptans, an 
intense yellowish-red colouration is produced, which appears as 
readily in presence of potassium niercaptide as with the free 
mercaptan. As an insoluble substance is formed, this reaction 
may be employed for the detection of chloropicrin (see p. 178). 

Chloropicrin oxidises hydrazine 3 even at the ordinary tempera- 
ture, evolving nitrogen. Tronov and Gershevich 4 have studied 
the velocity of the reaction between chloropicrin and hydrazine 
in various solvents (alcohol, ether, carbon disulphide, etc.). 

By the action of the sodium salts of the arylarsenious or 
alkylarsenious acids on chloropicrin in alcoholic solution, a reaction 
takes place which is first gentle and then very violent and leads 
to the formation of the following compounds 5 : 

/ONa Rv ,,0 

R-As< + CCl 3 NO„ = NaCl + >As( 

X ONa NG^ClaC/ X ONa 

R\ /y 0 / ONa 

>As( + 2 NaOH = RAsfO + CNaCLN0 2 + H 2 0 
0 2 C1 2 C/ \0Na ^ONa ^ 2 t 2 

Much data has been accumulated on the behaviour of chloro- 
picrin in contact with metals. According to Ireland, 6 chloropicrin 
attacks steel slightly and copper and lead very energetically. 
American publications, however, assert that chloropicrin attacks 
all metals. The corrosion of metals is confined to superficial 

1 Ray and Das, /. Chem. Soc, 1919, 115, 1308 ; 1922, 121, 323. 

2 Nekrassov and Melnikov, Bey., 1929, 62, 2091. 

3 A. K. Macbeth and J. D. Pratt, /. Chem. Soc, 1921, 119, 1356. 

4 Tronov and Gershevich, /. Rusk.fis. khim. obsc, 1928, 60, 171. 
6 Jaxubovich, /. prakt. Chem. (N.F.), 1933, 138, 159. 

6 Ireland, Medical Aspects of Gas Warfare, Washington, 1926, 298. 



TETRA CHLORODINITROETHANE 173 



staining, a layer being formed which protects the metal from 
further corrosion. 

Chloropicrin is one of the war gases most easily held back by 
active carbon. 1 

Fibrous materials absorb relatively little chloropicrin vapour 
and are not changed in resistance or colour. The absorbed 
chloropicrin may usually be removed by a current of dry air. 2 

Chloropicrin in vapour form strongly irritates the eyes. 
According to American observations (Fries), a man's eyes are 
closed after 3-30 seconds' exposure to an atmosphere containing 
2-25 mgm. chloropicrin per cu. m. of air. At a concentration of 
19 mgm. per cu. m. the eyes commence to lachrymate 3 and the 
limit of insupportability is about 50 mgm. per cu. m. 

Besides its irritant action, chloropicrin has a toxic and 
asphyxiating action. The mortality-product is 20,000 according 
to Prentiss, 4 and according to Ferri is 12,000 for dogs and 
cavies. 5 

3. Tetrachloro dinitroethane (M.Wt. 258) 

CC1 2 N0 2 

CC1 2 N0 2 

This substance was first prepared by Kolbe, 6 who did not, 
however, succeed in determining its physical and chemical 
characteristics. It was later obtained by Biltz, 7 by the action of 
fuming nitric acid,, or a mixture of nitric acid and concentrated 
sulphuric acid, on tetrachloroethylene. 

It may also be obtained by the action of anhydrous nitrogen 
peroxide on tetrachloroethylene at 10-12 atmospheres and 
6o° to 8o° C. for 3-6 hours (Biltz). 

Laboratory Preparation (Biltz) 

5 gm. tetrachloroethylene and about 8 gm. nitrogen peroxide 
are placed in a glass tube which is sealed off in the blowpipe and 
then heated at 100° C. for about 3 hours. After cooling, the 
tube is opened, the contents poured into a basin and the 
excess nitrogen peroxide allowed to evaporate off at room 
temperature. The solid white residue is then redissolved in warm 

1 H. S. Harned, /. Am. Chem. Soc, 1920, 42, 372 ; Herbst, Biochem. Z., 
1 92 1, 115, 204. 

2 Alexejevsky, /. Prikl. Khim., 1929, 1, 184. 

* D. Kiss, Z. ges. Schiess-Sprengstoffw., 1930, 25, 260, 300. 

4 A. Prentiss, Chemicals in War, New York, 1937, l6 - 

5 Ferri and Madesini, Giorn. di Medicina Militate, 1936. 
« H. Kolbe, Ber., 1869, 2, 326. 

* H. Biltz, Ber., 1902, 35, 1529. 



HALOGEN ATED NITRO- COMPOUNDS 



ligroin (not over 60° C.) and the tetrachlorodinitroethane 
crystallised out as plates. 

The nitrogen peroxide is prepared by drying the product 
obtained by the action of nitric acid on arsenious oxide by means 
of calcium nitrate and saturating it with oxygen. 

Physical and Chemical Properties 

It occurs as crystals which are decomposed by heating to 
130° C. with evolution of nitrogen peroxide. In a closed tube it 
melts at 142 0 to 143 0 C. 

It is volatile in steam and insoluble in water, but easily soluble 
in benzene and ether. It dissolves also in alcohol and in acetic 
acid. From these two solvents it may be reprecipitated by 
addition of water. 

It is not decomposed, even at the boiling point, by aqueous 
alkali solutions. With alcoholic potash it is converted into a 
crystalline substance of the formula 1 : 

CCLjNO., 
CCl(OK)N0 2 

Potassium cyanide causes complete breakdown of the molecule, 
and potassium carbonate, cyanogen chloride and carbon are 
formed. 

Heat is developed on adding an alcoholic solution of tetrachloro- 
dinitroethane to an aqueous solution of potassium iodide, and 
iodine separates as well as a crystalline substance : potassium 
tetranitroethane. 2 

Tetrachlorodinitroethane has powerful irritant 3 properties, and 
besides being about six times 4 as toxic as chloropicrin, has 
about eight times the lachrymatory power of the latter, according 
to Nekrassov. 

4. Bromopicrin. CBr 3 N0 2 (M.Wt. 298) 

Bromopicrin, or tribromonitromethane, was prepared in 1854 
by Stenhouse 5 while studying the action of bromine on picric 
acid. It was never employed as a war gas in the war of 1914-18. 

Preparation 
This compound may be obtained in various ways : 
(a) By the action of picric acid on " bromide of lime." 6 

1 Hoch and Kolbe, / prakt Chem , 1871, [2] 4, 60 

2 R Burrows and coll , / Chem Soc , 1932, 1360 
8 Hanzlik, / pharm exp Med , 1919, 14, 221. 

4 A Hoogeveen, Chemische Strijdmtddelen, The Hague, 1936. 

6 Stenhouse, Ann , 1854, 91, 307. 

6 Groves and Bolas, Ber , 1870, 3, 370. 



BROMOPICRIN : PROPERTIES 



175 



(b) By the action of bromine and potash on nitromethane. 1 

(c) By the action of bromine on nitranilic acid [i.e., ^-dinitro 
dihydroxy quinone). 2 

The most practical method of preparing bromopicrin in the 
laboratory is the following, according to Bolas and Groves 3 : 

Four parts of calcium oxide and 50 parts of water are mixed 
in a flask. Six parts of bromine are then added in small portions 
while the flask is shaken and externally cooled to prevent an 
excessive rise in temperature. One part of picric acid is then 
added and the mixture distilled under reduced pressure. The 
bromopicrin passes over in the first fractions of the distillate. It 
is separated from the water and dried over calcium chloride. 

Physical and Chemical Properties 

Bromopicrin forms prismatic crystals which melt at 10-25° C. 
and boil at 127° C. at 118 mm. pressure. 

Its specific gravity is 2-8n at 12-5° C. and 279 at 18 0 C. 4 

It is only slightly soluble in water, but dissolves easily in 
benzene, carbon tetrachloride, chloroform, alcohol and ether. 
Bromopicrin is precipitated from its alcoholic solution by the 
addition of water. 

It dissolves small quantities of iodine to form a violet solution. 

When heated rapidly at the ordinary pressure it decomposes 
with explosion. On heating to 130° C. it forms carbonyl bromide 
and nitrosyl bromide according to the equation : 

CBr 3 N0 2 -> COBr 2 + NOBr. 

In general, bromopicrin behaves chemically like chloropicrin, 
but is less stable to chemical reagents. By the action of brominat- 
ing agents it is converted into carbon tetrabromide (Bolas and 
Groves) . 

It reacts with potassium iodide variously according to the 
conditions of the reaction : 

CB r2 N0. 2 + 4 KI = CI 4 + KN0 2 + 3 KBr 
2 CBr 3 N0 2 + 6 KI = 3 I 2 -f- 2 C0 2 + N 2 -j- 6 KBr 

With potassium iodide and nitrite, iodine separates 6 : 

2 CBr 3 N0 2 + 6KI + 2KN0 2 = C 2 K 2 (N0 2 ) 4 + 6KBr + 3I2 
An alcoholic solution of potassium cyanide reacts with 

1 Meyer and Cherniak, Ann., 1875, 180, 122. 
8 Levy and Jedlicka, Ann., 1888, 249, 85. 

3 Bolas and Groves, Ann., 1870, 155, 253. 

4 Nekrassov, Khimija Otravliajuscikh Vescestv, Leningrad, 1929, 125. 
6 L. Hunter, /. Chem, Soc., 1922, 123, 543. 



176 HALOGEN ATED NITRO- COMPOUNDS 



bromopicrin in the cold to give, as final products of reaction, the 
potassium salt of symmetrical tetranitroethane and cyanogen 
bromide. 1 

Alcoholic solutions of bromopicrin precipitate silver bromide 
by the action of silver nitrate, slowly in the cold and rapidly on 
warming (Stenhouse). 

When bromopicrin is treated with a solution of potassium 
hydroxide (1 part KOH and 1-5 parts H 2 0) it first dissolves 
slowly and then decomposes as follows 2 : 

CBr 3 N0 2 + 6KOH = KN0 2 + K 2 C0 3 + 3KBr + 3H 2 0. 

or else, 

2CBr 3 N0 2 + 10KOH = 2K 2 C0 3 + N 2 + 5KBr + 5H 2 0 + KBr0 3 . 

It is not decomposed by cold sulphuric acid. 

Like chloropicrin, it reacts with hydrazine to evolve nitrogen. 3 

It also reacts with sodium ethylate, but very slowly. 4 Sodium 
or potassium sulphide react differently with bromopicrin, 
according to the conditions of the reaction. 5 

Bromopicrin vapour irritates the eyes : the minimum concentra- 
tion which causes irritation is 30 mgm. per cu. m. of air, according 
to Lindemann. 6 According to Mayer's researches, 7 bromopicrin 
has a toxic power only one-eighth to one-tenth of that of 
chloropicrin. 

Analysis of the Halogenated Nitro-compounds 

Detection of Chloropicrin 

The detection of chloropicrin is most simply carried out by 
direct sensory perception. 

Various methods have been suggested for the detection of 
chloropicrin by chemical means. None of these is as sensitive as 
perception by odour, according to Deckert. 8 

Method of Pyrogenic Decomposition. 9 One of the most widely 
used methods for the detection of chloropicrin in air consists in 
decomposing it by heat and then testing for chlorine in the 
products. 

1 Scholl and Brenneisen, Ber., 1898, 31, 642. 

• Wolff and Ruedel, Ann., 1897, 294, 202 ; N. Melnikov, /. Obscei Khim., 
Ser. A., 1936, 4, 1061. 

s A. K. Macbeth and J. D, Pratt, /. Chem. Soc, 1921, 119, 1356. 

• L. Hunter, loc. ext. 

5 Kretov, /. Obscei Khim., Ser. A, 1932, 2, 202. 

• Lindemann, Toksykologia chemicznych srodkow bojowych, Warsaw, 1925, 379. 
7 A. Mayer, Compt. rend., 1920, 171, 1396. 

• W. Deckert, Z. Hyg. Infektionskrankh., 1929, 109, 485. 

• A. C. Fieldner, Oberfell, etc., /. Jnd. Eng. Chem., 1919, 11, 519. 



CHLOROPICRIN : DETECTION 



The gas mixture is passed through a tube of quartz or porcelain 
heated almost to redness and the products of the decomposition 
are then bubbled through a solution containing potassium iodide 
and starch paste. If chloropicrin is present in the mixture under 
examination, chlorine will be liberated and this will liberate 
iodine from the potassium iodide and so colour the starch blue. 1 

Engel's " Inditator Apparatus " is based on a similar principle. 2 
It consists of a glass tube (see Fig. 12) through which passes a 




Fig. 12. 

silica rod which can be electrically heated to redness. The tube is 
connected with a special glass receiver inside which the stem of a 
tap-funnel projects so as to hold in suspension a drop of starch- 
iodide solution. The detection of chloropicrin in air is carried out 
by passing the gas to be examined through the apparatus. If 
chloropicrin is present, the hanging drop of starch-iodide solution 
will be coloured blue. 

The sensitivity of this reaction depends very much on the age 
of the starch solution and it is advisable to use a recently prepared 
solution. 3 

The Flame Test. Another method of detection, also based on 
the pyrogenic decomposition of chloropicrin, consists in passing 
the gas mixture to be examined into a gas jet, the flame of which 
maintains a copper spiral at red heat. 4 

This flame, in presence of even 0-25 mgm. chloropicrin per litre 
of air, is coloured green (Krczil). 

Ray and Das's Method. 5 This method of detection is based on 

1 This method of detecting chloropicrin was employed to determine the 
duration of the protection afforded by anti gas niters against mixtures of air and 
chloropicrin. Dubinin, /. Prikl. Khim. 1931, 1109. 

8 Engel, Z. ges. Schtess Sprengstoffw., 1929, 24, 451. 

8 F. Krczil, Untersuchung und Beweriung Technicher Adsorptionsstoffe, 
Leipzig, 1 93 1, 422. 

* See p. 40 of the present book, and Lamb, /. Am. Chem. Soc, 1920, 42, 78. 
6 Ray and Das, /. Chem. Soc, 1919, 115, 1308 ; 1922, 121, 393. 



178 HALOGEN ATED NITRO- COMPOUNDS 



a reaction recently discovered by Ray and Das, according to which 
chloropicrin, in reacting with the potassium salts of mercaptans, 
forms insoluble condensation products. 

According to Nekrassov, 1 in this method the gas to be tested is 
passed through an alcoholic solution of the potassium salt of 
dithioethylene glycol. In the presence of chloropicrin a yellow 
precipitate, m.p. 123° C, separates. 

This method may also be conveniently applied to the quantita- 
tive determination of chloropicrin, since the chlorine in the 
chloropicrin molecule is quantitatively converted into potassium 
chloride. 

Sodium Ethylate Method. This method consists in decomposing 
chloropicrin with sodium ethylate (see p. 171) and then proceeding 
to the detection of the sodium nitrite or chloride formed in the 
reaction : 

CC1 3 N0 2 + 4C 2 H 5 ONa = C(OC 2 H 5 ) 4 + 3 NaCl + NaN0 2 . 

By means of this reaction chloropicrin may be detected at a 
concentration of about 6 mgm. per cu. m. of air, according to 
Ireland. 2 

Dimethylaniline Paper. The detection of chloropicrin by 
means of this paper depends on the change in colour from white to 
yellow or maroon which takes place in presence of this gas. 

The dimethylaniline papers are prepared by soaking strips of 
filter paper in a 10% solution of dimethylaniline in benzene. 3 

If the concentration of chloropicrin is low, the colour change 
may be seen when the paper is moved about in the gaseous 
atmosphere. Chlorine, bromine and nitrous gases also produce 
a colour-change with this paper, but of a different shade from 
that with chloropicrin. 4 

Thiophenol Method. This method consists in passing the gas 
mixture to be tested through an alcoholic solution of thiophenol. 
In the presence of chloropicrin a white precipitate or opalescence 
forms. 5 A turbidity appears in 3-4 minutes with 1-2 litres of 
the gas containing about 60 mgm. chloropicrin per cu. m. 6 

Alexejevsky's Method. This depends on the reduction of 
chloropicrin by metallic calcium to form nitrous acid, which is 
detectable by the Griess reaction. 7 

1 Nekrassov, Voina i Tecnica, 1926, 275, 32. 
a Ireland, op. ext., 298. 

3 Deckert, Z. Hyg. Infektionskrankh., 1929, 109, 485 ; Z . anal. Chem., 1938, 
113, 183. 

4 Hennig, Gasschutz und Luftschuti, 1937, I 9- 




" Pancenko, op. cit. 

' Alexejevsky, /. Khim. Promise!., 1931, 8, 50. 



CHLOROPICRIN : DETERMINATION 



The gas mixture under examination is passed through a wash- 
bottle containing ethyl alcohol and the solution obtained then 
treated with metallic calcium. The nitrous acid which is formed 
is then identified with sulphanilic acid and a napthylamine. In 
the presence of chloropicrin a red precipitate is produced. 
Sensitivity, 2 mgm. of chloropicrin. 

This reaction cannot be used for the quantitative determination 
of chloropicrin. 

Other Colour Reactions. On boiling the substance to be tested 
with an alcoholic solution of potassium hydroxide and then 
adding a few ml. of thymol, a yellow colouration appears in the 
presence of chloropicrin and this changes to reddish-violet on 
addition of sulphuric acid. 

Substitution of resorcinol for thymol gives a red colouration. 1 

Quantitative Determination 

Gas Volumetric Method of Dumas. The quantitative 
determination of chloropicrin may be carried out by decomposing 
the sample to be examined and measuring the volume of the 
nitrogen formed by the volumetric method of Dumas. In employ- 
ing this method it is advisable 2 to use a very long combustion 
tube with its front part filled for 8-10 cm. with a mixture of 
copper turnings and reduced copper. It is also best to carry out 
the combustion as slowly as possible so as to prevent the nitrogen 
peroxide from escaping decomposition. 

Sodium Sulphite Method. 3 This method is based on the 
reaction between sodium sulphite and chloropicrin already 
mentioned : 

CC1 3 N0 2 + 3Na 2 S0 3 + H 2 0 = CHN0 2 (S0 3 Na) 2 + 3NaCl + NaHS0 4 

In practice this determination is carried out by adding to a 
weighed quantity of the chloropicrin in a small flask fitted with 
a condenser, an excess of an aqueous-alcoholic solution of sodium 
sulphite, prepared by dissolving 10 gm. sodium sulphite in 
250 ml. water and diluting with an equal volume of ethyl alcohol. 
The liquid in the flask is then carefully heated so as to distil 
off all but about 10 ml. This is then diluted with water to 100 ml. 
and 10 ml. of nitric acid and an excess of a standardised solution 
of silver nitrate are added. The solution is then warmed to drive 
off the nitrous gases and to coagulate the silver chloride, and 
then cooled and the excess silver nitrate titrated with a solution 
of ammonium thiocyanate (ferric alum indicator). 

1 Guillemard and Labat, Bt4l. soc. pharm. Bordeaux, 1919. 
8 Stenhouse, Ann., 1848, 66, 245. 

8 Thompson and Black, /. Ind. Eng. Chem., 1920, 12, 1067. 



l8o HALOGEN ATED NITRO- COMPOUNDS 



This method, according to Aksenov, 1 may be applied to the 
determination of chloropicrin vapour in air. A measured volume 
of the air is passed through an aqueous alcoholic solution of 
potassium sulphite, the latter then boiled and the amount of 
chloride determined by Yolhard's method. 

Sodium Peroxide Method. This method consists in 
decomposing the chloropicrin with sodium peroxide and then 
volumetrically determining the chlorine liberated in the reaction. 2 

A measured volume of the gas mixture to be examined is 
passed through a wash-bottle containing 50 ml. of a 1% solution 
of sodium peroxide in 50% ethyl alcohol prepared in the following 
manner : 2 gm. sodium peroxide is dissolved in 100 ml. iced 
water and just before using 25 ml. of this solution is diluted 
with 25 ml. 95% alcohol. 

The chloropicrin, on coming into contact with the alcoholic 
solution of sodium peroxide, decomposes, forming sodium 
chloride, which may be determined volumetrically with a N/100 
solution of silver nitrate (using potassium chromate as indicator), 
after neutralising the alcoholic solution with sulphuric acid (to 
the phenolphthalein end-point). 

The number of ml. of silver nitrate solution used multiplied 
by 0-546 gives the quantity of chloropicrin in mgm. present in 
the volume of air passed through the sodium peroxide solution. 

This method of analysis was also used by Dubinin 3 for the 
determination of chloropicrin in the gas mixtures prepared for 
the testing of activated carbons. 

1 Aksenov, Metodica Toksikologii boevikh otravliajuscikh Vescestv, Moscow, 
1931. 95. 

s Fieldner and coll., /. Ind. Eng. Chem., 1919, 11, 519. 
* Dubinin, /. Prikl. Khim., 193 1, 1100. 



CHAPTER XIII 



CYANOGEN DERIVATIVES 

The war gases belonging to the class of cyanogen derivatives 
are characterised by the presence of the CN — radicle in their 
molecules. It has been found that this radicle may have one of 
the following two formulae : 

— C=N — N=C 

The first of these formulae seems less suitable than the second 
for these war gases, which like the mono- and di-halogenated 
derivatives of acetylene (see p. 45), have properties more in 
keeping with the presence of a divalent carbon atom. It may 
be concluded that it is the presence of this divalent carbon atom 
rather than that of the nitrogen atom which accounts for the 
toxicity of this radicle. The bivalent carbon atom has in fact 
great chemical reactivity and is the point of attack in all chemical 
and biochemical reactions. 

Among the various compounds containing the CN group which 
were employed in the war of 1914-18, hydrocyanic acid, phenyl 
carbylamine chloride and the cyanogen halides, particularly 
cyanogen bromide, were most widely used. 

The cyanogen halides may be considered as derivatives of 
hydrocyanic acid in which the hydrogen atom is substituted by 
a halogen atom. According to some authorities the aggressive 
power of these compounds is greater than that of hydrocyanic 
acid, for besides their toxic properties, due to the presence of the 
CN — group, they have an irritant action due to the presence of 
the halogen. 

Various other compounds containing the CN — radicle were 
studied towards the end of the war and since that period. Of 
these, chlorobenzyl cyanide, bromobenzyl cyanide, diphenyl 
cyanoarsine, phenarsazine cyanide, etc., were used to a consider- 
able extent as war gases. Recently cyanogen fluoride has also 
been prepared and studied. It is a colourless gas with powerful 
lachrymatory properties. 

1. Hydrocyanic Add. HCN (M.Wt. 27) 

Hydrocyanic acid was discovered by Scheele in 1782. He noted 
that it was extremely toxic, but it was scarcely used as a war gas 

181 



182 



CYANOGEN DERIVATIVES 



during the war of 1914-18 because of its high vapour tension 
and its rapid diffusion. 

Only the French used it, and not more than 4,000 tons were 
employed during the whole war period. 

Hydrocyanic acid may be prepared in various ways ; by 
passing electric sparks through a mixture of acetylene and 
nitrogen, 

C 2 H 2 + N 2 = 2HCN 
or by heating' chloroform with ammonia, 

/CI H\ 
H-Cf CI + H-)N = 3 HC1 + HCN 
\C1 H/ 

The method most commonly used, especially if it is desired 
to prepare anhydrous hydrocyanic acid, consists in decomposing 
a cyanide with an acid (hydrochloric, sulphuric, hydrosulphuric, 
carbonic, etc.). 

KCN + HC1 = KC1 + HCN 
Hg(CN) 2 + H 2 S = HgS + 2 HCN 

Laboratory Preparation 1 

100 gm. potassium cyanide, as free as possible from carbonate 
and in pellet form, are placed in a flask fitted with a tap-funnel 
and a delivery tube. The delivery tube leads to two U tubes 
in series which are filled with a mixture of fused and granular 
calcium chloride, and immersed in a water-bath at 35° C. The 
second of these tubes may be connected to two more U tubes, the 
first of which is maintained at about — io° C. 2 in a freezing 
mixture and the second at + 20° C. Each of these tubes, which 
are designed to receive the condensate of hydrocyanic acid 
formed in the reaction, is fitted at the bottom with a glass lead-off 
tube. This is connected through a glass cock to a cooled flask 
in which the liquid hydrocyanic acid collects. 

Before the preparation is commenced it is advisable to pass a 
current of dry air through the whole of the apparatus. Cooled 
aqueous sulphuric acid (1 : 1) is allowed to drop slowly through 
the tap-funnel on to the potassium cyanide, regulating the rate 
of addition so that 1 drop of hydrocyanic acid condenses in the 
first receiver every second minute. Towards the end of the 
operation it may be necessary to heat the contents of the flask 

1 Made and Panting, /. Chem. Soc, 1898, 73, 256. 

* It is advisable not to cool below — io°, otherwise the hydrocyanic acid 
solidifies and prevents the gas passing. 



HYDROCYANIC ACID: PREPARATION 183 



almost to boiling in order to maintain the evolution of hydrocyanic 
acid. 

The greater part of the hydrocyanic acid produced in the 
reaction condenses in the first U tube and is collected in the 
corresponding flask. 

According to Slotta, 1 in order to maintain a regular evolution 
of hydrocyanic acid it is advisable to add about 40% ferrous 
sulphate to the sulphuric acid and to run a recently prepared 
solution of potassium cyanide on to the sulphuric acid (1 : 1) 
which is meanwhile maintained at 50 0 C, rather than to add the 
sulphuric acid to the potassium cyanide. The evolution tube 
for the hydrocyanic acid should also be connected to the following 
apparatus : 

(a) A condenser, in which water vapour and part of the 
hydrocyanic is condensed. 

(b) A wash-bottle containing 20 ml. 2 N. sulphuric acid 
maintained at 50 0 C. in a bath. 

(c) A wash-bottle containing glass-wool and 200 gm. calcium 
chloride, maintained at 50 0 C. in a bath. 

(d) A receiver, cooled externally with ice and salt, in which 
the hydrocyanic acid collects. 

In storing liquid hydrocyanic acid it is advisable to add 2 drops 
of concentrated sulphuric acid and to wire on the stopper of the 
bottle. 

In order to prepare hydrocyanic acid for producing a definite 
concentration of the gas in the air, 2 for example 1% by volume 
in a space of 100 cu. m. capacity, 2-6 litres of 60° Be\ sulphuric 
acid are added to 4^4 litres of water at 50 0 to 6o° C, then, while 
still hot, 275 kgm. sodium cyanide are added as rapidly as 
possible. 

Industrial Preparation 

Until a few years ago, hydrocyanic acid was always prepared 
by heating potassium ferrocyanide with dilute sulphuric acid. 
Nowadays, it is preferred to employ the alkali cyanides, either 
sodium or potassium, as these are manufactured synthetically 
on a large scale and very cheaply. Usually 50% aqueous sulphuric 
acid is run on to sodium cyanide either in concentrated solution 
or in lumps, and then the mixture heated in order to drive off the 
hydrocyanic acid. As it is evolved, the acid is dried by passing 
through calcium chloride and then liquefied by passing it first 

1 K. Slotta, Ber., 1934, 67, 1030. 

» Sieverts and Hermsdorf, Z. angew. Chem., 1921, 34, 5. 



CYANOGEN DERIVATIVES 



through a coil immersed in water at 15° C. and then through a 
coil in brine at 0° C. 

Several other methods are now employed industrially for the 
preparation of hydrocyanic acid. Synthesis from the elements 
is widely used. In this a mixture of hydrogen, carbon monoxide 
and nitrogen is passed through an electric arc, mixtures of 
nitrogen and hydrocarbons being sometimes employed, e.g., 20% 
methane, 10% hydrogen 2nd 70% nitrogen. 

Also the formation of hydrocyanic acid from spent fermentation 
wash may be mentioned. This material is obtained from molasses, 
which, after fermenting and distilling, leaves a residue which still 
contains about 4% nitrogen as betaine. On further distilling 
this spent wash to about 40° Be\ the evolved gas, after separating 
from the tar by cooling, is passed through a superheater consisting 
of a quartz tube heated to about i,ooo° C. In this way the nitro- 
genous compounds are converted to ammonia and hydrocyanic 
acid. The gas issuing from the superheater is washed with 
sulphuric acid to remove ammonia, while the hydrocyanic acid 
is taken out in an alkaline absorbent. By this means about 50% 
of the nitrogen of the spent wash is converted into ammonia and 
hydrocyanic acid, while the other half is lost as elementary 
nitrogen. 

Physical and Chemical Properties 

Pure anhydrous hydrocyanic acid is a clear colourless liquid 
with a peculiar odour which is usually compared with that of 
bitter almonds. It has been observed, however, that this 
substance has an indefinite odour which varies with the degree 
of its dilution with air and the period of exposure to it. 1 

The vapour from the pure liquid or concentrated aqueous 
solution causes an irritation at the back of the throat and a 
bitter taste in a short time. Diluted with air it is not very 
irritant, but has a less disagreeable odour which is somewhat 
aromatic. It is a peculiar property of this substance that even in 
minute quantity it paralyses the nerves of odour and taste, and 
after a few seconds the first sensitivity to the odour is lost. 

It boils at 26-5° C, and solidifies on cooling at — 13*4° C, 
forming a crystalline mass which melts at — 15° C. 

If liquid hydrocyanic acid is coloured yellow or brown, it may 
be considered as being less dangerous, because it is in process of 
alteration. The commercial product should be colourless and 
contain 96-98% of hydrocyanic acid, the balance being water. 

In the gaseous state it is colourless with a vapour density of 

1 Anon., Die Gasmaske, 1935, Nos. 4-5. 



HYDROCYANIC ACID : PROPERTIES 185 



0-948 ; that is, 1 litre of gaseous hydrocyanic acid weighs I-2I gm. 
at 0° C. and 760 mm. The specific gravity of liquid hydrocyanic 
acid is 07058 at f C. and 0-6969 at 18 0 C. The coefficient of 
thermal expansion between o° C. and 15 0 C. is 0-0019. The 
critical temperature is 138-5° C. and the critical pressure 53-3 
atmospheres. The heat of vaporisation is 210-7 cals. per gm. 
By spontaneous evaporation the current of air produced passes 
over the surface of the hydrocyanic acid, lowering the temperature 
to that of freezing (— 13-4° C). 
The vapour tension at various temperatures is as follows 1 : 



Its volatility at 20° C. is 873,000 mgm. per cu. m. 

Because of its high vapour tension as well as its low density it 
is difficult to maintain a high concentration of hydrocyanic acid 
in an open place. As the toxic action is considerably reduced 
by dilution, numerous artifices were used during the war to 
render this gas more persistent. Lebeau, in France, suggested 
mixing it with the smoke-producing chlorides, as stannic, 
titanium or arsenic chloride. The result was that the already 
low stability of the hydrocyanic acid was still further reduced. 
Then it was proposed to add a proportion of chloroform to the 
mixture, this forming the mixture termed " Vincennite " by the 
French. It consisted of 50% hydrocyanic acid, 30% arsenic 
trichloride, 15% stannic chloride and 5% chloroform. 

Hydrocyanic acid is miscible in all proportions with alcohol, 
ether, glycerol, chloroform, benzene, tricresyl phosphate, etc. It 
does not dissolve nitro-cellulose, but cellulose acetate and the 
other cellulose esters are soluble. Gums, rubber and gelatin are 
not dissolved. Carbon dioxide and hydrogen sulphide are slightly 
soluble and sulphur dioxide is soluble in all proportions. 2 

It dissolves in water to form a solution which has a weak acid 
reaction and is unstable in time. The dissolved hydrocyanic 
acid partly forms a brown flocculent substance and partly 

1 Bredig and Teichmann, Z. Elektrochem., 1925, 31, 449 ; M. Linhard, 
Z. anorg. Chem., 1938, 236, 207. 

8 Buchanan, Chim. et Ind., 1932, 28, 1026. 



TEMPERATURE 

°C. 



VAPOUR TENSION 
MM. MERCURY 



— IO 
O 



25-6 



4 

io-8 
14-8 
18-0 



165 
256 
380 
427 
504 
567 
757 



CYANOGEN FLUORIDE 



187 



Hydrocyanic acid reacts with benzoyl chloride in presence of 
pyridine, benzoyl cyanide being formed 1 : 

C 6 H 6 C0C1 + HCN = C 6 H 8 COCN + HC1. 

Benzoyl cyanide forms crystals melting at 33 0 C. and boiling at 
206° to 208 0 C. It is decomposed by water. 

Hydrocyanic acid forms additive compounds with several 
inorganic salts, such as the following : 

Stannic chloride forms SnCl 4 .2HCN. 
Titanium chloride „ TiCl 4 ,2HCN. 
Zinc chloride „ ZnCl^HCN. 

It can be transported in the liquid condition in metal containers, 
for example, in tinned-iron cans, which are cooled with ice in 
summer, or in iron cylinders, like the compressed gases (Buchanan) . 

The lower limit of sensitivity to the odour is about 1 mgm. per 
cu. m. of air. 2 

It is a powerful poison, but the human body is capable of 
neutralising the effects of the gas within certain limits. Thus 
in a concentration of about 30 mgm. per cu. m. hydrocyanic 
acid is eliminated from the human organism as rapidly as it is 
absorbed and so no dangerous consequences follow. At higher 
concentrations, however, poisoning is rapid. 

The lethal concentration, according to Flury, is 120-150 mgm. 
per cu. m. of air for hour's exposure, while, according to 
Prentiss, it is 200 mgm. per cu. m. for 10 minutes' exposure and 
150 mgm. per cu. m. for 30 minutes' exposure. 

2. Cyanogen Fluoride. CNF (M.Wt. 45) 

Moissan attempted to prepare this substance by acting on 
cyanogen with fluorine. 3 A very violent reaction took place 
without any deposition of carbon. 

Recently cyanogen fluoride has been prepared by Cosslett 4 by 
the action of silver fluoride on cyanogen iodide : 

AgF + CNI = Agl + CNF. 

It may also be prepared in lower yield by the action of silver 
fluoride on cyanogen bromide, but in this case it is always impure 
with brominated products. 

1 Claisen, Ber., 1898, 31, 1024. 

2 Smolczyk, Die Gas-Maske, 1930, 32. 

s H. Moissan, Le Fluor et ses composes, 19 00 . I 3&- 
* V. Cosslett, Z. anorg. Chem., 1931, 201, 75. 



i88 



CYANOGEN DERIVATIVES 



Preparation 

i -3 gm. silver fluoride is powdered in a mortar with 1-5 gm. 
cyanogen iodide and transferred to a Jena glass tube about 
50 cm. long and 2-5 cm. diameter. After evacuating the tube it 
is sealed off in the blowpipe and then heated in a furnace to 
220° C. for 2\ hours. After cooling, the tube is immersed in 
liquid air and the products allowed to condense. The tube is then 
opened and the contents distilled at — 70° C. in a freezing 
mixture of acetone and carbon dioxide. Yield 20-25% (Cosslett). 

Properties 

Cyanogen fluoride is a colourless gas at normal temperature, 
and on cooling to a low temperature it forms a white pulverent 
mass which sublimes at — 72 0 C. at atmospheric pressure. 

It is insoluble in water. In glass vessels it is stable and does not 
attack mercury. However, after storing for about a week in 
glass containers it attacks the surface ; this is attributed to the 
action of light. 

3. Cyanogen Chloride. CNC1 (M.Wt. 61-47) 

Cyanogen was discovered by Wiirtz and prepared for the first 
time by Berthollet. 1 It was used during the war by the French 
(October, 1916) both alone and in admixture with arsenic 
trichloride (" Vivrite "). 

Laboratory Preparation 2 

It is prepared by the action of chlorine on potassium cyanide. 

About 100 ml. of a solution of chlorine saturated at 0° C. are 
placed in a 300-ml. flask and cooled while a solution of potassium 
cyanide is allowed to flow in slowly from a tap-funnel until the 
yellow colour of the chlorine disappears. The liquid is again 
saturated with chlorine and further potassium cyanide added 
still slowly, taking care not to add an excess, which causes 
decomposition of the cyanogen chloride. The latter is then 
liberated from the aqueous solution by warming on the water-bath 
to 6o° to 70 0 C. 

According to Held, 3 in order to prevent the formation of 
paracyanogen, a secondary product in the reaction between 
chlorine and potassium cyanide, it is advisable to add to the 
latter 1 molecule of zinc sulphate per 4 molecules of the cyanide. 

1 Berthollet, Ann. chim.phys., 1802, [1] 35, 1789. 

2 Hantzsch and Mai, Ber., 1895, 28, 2.171 ; Zappi, Bull. soc. chim., 1930, 
[4] 47, 453 ; Jonescu, Antigaz, 1932, 6, Nos. 1-2, 17. 

3 Held, Bull. soc. chim., 1897, [3] 17, 287. 



CYANOGEN CHLORIDE 



Industrial Manufacture 

Cyanogen chloride is also prepared industrially by the reaction 
of chlorine on sodium cyanide. 1 

Two solutions are added to a large iron vessel fitted with 
cooling coils, one of sulphuric acid and the other of sodium 
cyanide. After cooling, chlorine is bubbled in. At the end of 
the reaction, the cyanogen chloride is distilled off and purified 
from the gaseous reaction products by passing it through a series 
of purification towers, two containing calcium chloride to remove 
traces of moisture and one containing pumice and arsenic to 
remove the chlorine still present. Yield 80%. 

Physical and Chemical Properties 

Cyanogen chloride is a colourless, very volatile liquid, which 
boils at 12-5° C. and solidifies at — 6-5° C. (Mauguin). Its 
specific gravity is 1-2 and its vapour density 2*1. It is very 
soluble in water (1 volume water at 20° C. dissolves 25 volumes 
cyanogen chloride) and in the organic solvents such as alcohol, 
ether, etc. 2 The alcoholic solution easily decomposes. 

The vapour tension of cyanogen chloride at various temperatures 
is given in the following table 3 : 

TEMPERATURE VAPOUR TENSION 

0 C. MM. MERCURY 

— IO 270-5I 

o 444*11 

10 681-92 

20 1,001-87 

30 1,427-43 

Its volatility at 15° C. is 2,600,000 mgm. per cu. m. and at 
20° C. is 3,300,000 mgm. per cu. m. 

The heat of volatilisation at o° C. is 109 cals., while at 12-5° C. 
it is 135. The coefficient of thermal expansion at 0° C. is 0-0015. 

It has a low stability and is gradually transformed into its 
trimer, cyanuryl chloride, (CNC1) 3 , a crystalline substance 
melting at 190° C. and having a specific gravity of 1-32. It is 
soluble in ether, chloroform, etc. 4 Biologically, it is almost 
inactive. In order to impede this transformation, the French 
mixed cyanogen chloride with arsenic chloride. Water, chlorine 
and hydrochloric acid tend to favour the polymerisation. 5 

1 Mauguin and Simon, Compt. rend., 1919, 169, 383 ; Ann. Mm. 1921, 
15, 18. 

• Serullas, Ann. chim. phys., [2] 35, 342. 

* Regnault, Jahresber. u. fortschr. Chem., 1863, 65 ; Klemenc, Z. anorg. 
Chem., 1938, 235, 429. 

4 Nef, Ann., 1895, 287, 358. 

» Wurtz, Ann., 1851, 79, 284 ; Naumann, Ann., 1870, 155, 175. 



CYANOGEN DERIVATIVES 



Water slowly hydrolyses cyanogen chloride, forming cyanic 
acid and hydrochloric acid : 

CNC1 + H 2 0 HCNO + HC1. 

This reaction is accelerated by the alkali hydroxides. 1 Cyanogen 
chloride reacts quantitatively with an alcoholic solution of 
ammonia to form cyanamide 2 : 

CNC1 + 2NH3 = NH 2 CN + NH 4 C1. 

By the action of alkaline reducing agents, like sodium sulphite 
with sodium hydroxide, sodium cyanide, sodium chloride and 
sodium sulphate are formed. 

When hydriodic acid is added to an aqueous solution of 
cyanogen chloride at ordinary temperatures, iodine is liberated. 
The amount set free increases slightly on standing, but more 
rapidly on heating to about 100° C, reaching a maximum at 80% 
of that required by the equation (Chattaway) : 

CNC1 + 2HI = HCN + HC1 + I 2 . 

On heating an aqueous solution of hydrogen sulphide with a 
solution of cyanogen chloride to about 100° C, sulphur separates, 
while the hydrocyanic acid which is formed is partly hydrolysed 
and partly combines with the sulphur, forming thiocyanic acid. 

Aqueous solutions of cyanogen chloride do not react with 
silver nitrate, 3 but aqueous-alcoholic solutions form silver chloride. 4 
Unlike cyanogen bromide, the Prussian blue reaction does not 
take place with cyanogen chloride. 5 

It has practically no corrosive action on iron, lead, aluminium, 
tin or silver. It does attack copper and brass slightly, however, a 
protective coating being formed which prevents further corrosion. 

Commercial cyanogen chloride contains 2-5% of hydrocyanic 
acid. 

It may be mixed with chloropicrin and with dichloroethyl 
sulphide without change. 

It is added to " Zyklon B " (see p. 104) both to prevent the 
polymerisation of the hydrocyanic acid present and also to act 
as a warning substance. 6 

Concentrations of 2-5 mgm. per cu. m. of air produce abundant 

1 Chattaway and Wadmore, /. Chem. Soc, 1902, 81, 191. 

2 Cloez and Cannizzaro, Ann., 1851, 78, 229. 

3 Serullas, Berzelius Jahresber, 8, 90. 

4 E. Zappi, Rev. de Ciencias Quimicas. Uyiiv. La Plata, 1930, 7. 
6 E. Zappi, Bull. soc. chim., 1930, [4] 47, 453. 

• Rimarsky and coll., Jahresber. Chem. Techn. Reichsanstalt,, 1930, 8, 71. 



CYANOGEN BROMIDE 



191 



lachrymation in a few minutes. The maximum concentration 
which a normal man can support, without damage for 1 minute is 
50 mgm. per cu. m. of air (Flury). 

The lethal concentration for 10 minutes' exposure is 400 mgm. 
per cu. m. (Prentiss). 

4. Cyanogen Bromide. CNBr (M.Wt. 105 93) 

Cyanogen bromide was first employed by the Austrians in 

September, 1917, both in benzol solution and in admixture with 

bromoacetone and benzol. 

It was first prepared by Serullas in 1827. 1 It is obtained by 

the action of bromine on potassium cyanide, similarly to cyanogen 

chloride. 

Laboratory Preparation 2 

150 gm. bromine and 50 ml. water are placed in a flask fitted 
by means of a three-holed stopper with a tap-funnel, a condenser 
and a thermometer. A solution of 65 gm. potassium cyanide in 
120 ml. water, cooled to o° C, is introduced through the tap- 
funnel gradually (about 1 drop per second), into the flask 
which is also cooled to about 0° C. and agitated. As soon 
as the red colour of the bromine commences to pale, the cyanide 
solution remaining in the tap-funnel is diluted to about double its 
volume and added carefully, avoiding an excess, which would 
cause the decomposition of the cyanogen bromide with formation 
of azulmic products, darkening the colour of the mass. 

At the end of the reaction the contents of the flask are 
transferred to a retort, which is partly filled with calcium chloride 
and stoppered, and then warmed on the water-bath at 65-70 0 C. 
The cyanogen bromide distils over and condenses in white 
needles, which may be purified further by redistilling over 
calcium chloride. The yield is about 90%. 3 

Industrial Manufacture 

In the preparation of cyanogen bromide from bromine and 
sodium cyanide there is a loss of half of the bromine as sodium 
bromide 4 : 

NaCN + Br a = NaBr + CNBr. 
In order to avoid this loss, sodium chlorate is generally added, 

1 Serullas, Ann. chim. phys., 1827, [2] 34, 100. 

2 Scholl, Ber., 1896, 29, 1822 ; Grignard, Bull. soc. chim., 1921, 29, 214. 

3 K. Slotta, Ber., 1934, 67, 1029. 

* V. Grignard and P. Crouzier, Bull. soc. chim., 1921, 29, 214. 



192 



CYANOGEN DERIVATIVES 



as in the preparation of the halogenated ketones (see p. 147). 
The following reaction takes place : 

NaClO, + 3NaBr + 3 NaCN + 6H,S0 4 = 3 CNBr + NaCl + 

6NaHS0 4 + 3H g 0. 

The manufacture of cyanogen bromide is carried out in large 
metal vessels in which a solution of the three salts is first prepared. 
30% sulphuric acid at a temperature of 30°C. is then slowly run 
in. At the end of the reaction the product is separated by 
distillation. Yield 75%.* 

Physical and Chemical Properties. 

Cyanogen bromide forms transparent crystals which are either 
acicular or prismatic. It has a penetrating odour and melts at 
52° C. Its boiling point at 750 mm. is 61-3° C. Its specific gravity 
is 1-92 and its vapour density 3-6. The vapour tension at any 
temperature may be calculated by means of the following formula 
(see p. 5) : 

1 j. « 2457,5 
log p = 10.3282 

273 + t 

Baxter and Wilson 2 give the following experimental values : 

TEMPERATURE VAPOUR PRESSURE 

0 C. MM. MERCURY 

-15 6-3 

O 21-2 

15 63-3 

25 119-5 

35 223-5 

The volatility at 16 0 C. is about 155,000 mgm. per cu. m. and 
at 20 0 C. about 200,000 mgm. per cu. m. 

It is only sparingly soluble in water, but more readily in 
alcohol, ether, carbon disulphide, acetone, benzene and carbon 
tetrachloride. 

The chemical behaviour of cyanogen bromide is very similar 
to that of cyanogen chloride. For instance, like the chloride it 
polymerises in time to the trimer, (CNBr) 3 . 3 This polymer is 
reconverted to cyanogen bromide by heat, so that in order to 
purify polymerised cyanogen bromide it is merely necessary to 
distil it. 

It is decomposed by water, slowly at ordinary temperatures, 

1 For more detailed descriptions of the. industrial manufacture of cyanogen 
bromide, see Chem. Zentr., 1907 (I), 591, and 1908 (I), 1807. 
a Baxter and Wilson, /. Amer. Chem. Soc, 1920, 42, 1389. 
8 Ponomarev, Ber., 1885, 18, 3261. 



CYANOGEN BROMIDE: PROPERTIES 193 



but more rapidly at 100° C. The products of hydrolysis are 
similar to those formed from cyanogen chloride. It reacts with 
sodium or potassium hydroxide forming sodium or potassium 
bromide and cyanate 1 : 

CNBr + 2 NaOH = NaCNO + NaBr + H 2 0. 

With an aqueous solution of ammonia it is quantitatively 
converted to ammonium bromide and cyanamide, as follows : 

CNBr + 2NH3 = NH 4 Br + NH 2 CN. 

This reaction may be used for the quantitative determination 
of cyanogen bromide, according to Oberhauser 2 (see p. 209). 

By the action of the alkali sulphides on cyanogen bromide, the 
corresponding thiocyanates are formed according to the following 
equation 3 : 

CNBr + K 2 S = KSCN + KBr. 

With various other substances cyanogen bromide reacts as 
vigorously as does cyanogen chloride. For instance, even at 
ordinary temperatures iodine is liberated from hydriodic acid 
and sulphur from hydrogen sulphide, while sulphurous acid is 
oxidised to sulphuric acid : 

CNBr + 2 HI = I 2 + HBr + HCN 

CNBr + H 2 S = S + HBr + HCN 

CNBr + H 2 S0 3 + H 2 0 = H 2 S0 4 + HBr + HCN 

All these reactions take place quantitatively, but that with 
hydriodic acid is somewhat slow. 4 

On treatment of cyanogen bromide with tertiary amines, 
additive products of the following general formula are produced : 

Ri\ / Br 

R 3 / N CN 

These are not stable and decompose with formation of alkyl 
bromide and dialkyl cyanamides, as follows : 

R lV /Br R 2 \ 
R 2 4n( RiBr+ >N-CN 

R3/ X CN R 3 X 

A similar reaction takes place with the tertiary arsines. 5 

1 Serullas, Ann. chim. phys. 1827, [2] 35, 345 ; Nef, Ann., 1895, 287, 316. 

2 F. Oberhauser and J. Schormuller, Ber., 1929, 62, 1439. 

3 Gutmann, Ber., 1909, 42, 3627. 

* R. Mooney, /. Chem. Soc, 1933, 1319. 

4 Steinkopf, Ber., 1921, 54, 2791. 



194 



CYANOGEN DERIVATIVES 



By the action of cyanogen bromide on pyridine in alcoholic 
solution m the cold, a reddish-brown colouration is formed and 
white crystals separate 1 

Cyanogen bromide has a powerfully corrosive effect on metals, 
attacking copper, iron, zinc, aluminium, and in time even lead 
and brass 2 

Unlike cyanogen chloride, the bromide is not miscible with 
dichloroethyl sulphide, but reacts with it. It is, however, 
miscible with chloropicrin. 

During the war of 1914-18 it was employed in solution in 
benzene and bromoacetone in the following proportions • cyanogen 
bromide 25%, bromoacetone 25%, benzene 50%. This mixture 
was known as " Campielhte." 

Concentrations of 6 mgm. per cu. m. cause strong irritation 
of the conjunctiva and of the mucous membranes of the respira- 
tory system The limit of insupportability, that is, the maximum 
concentration which a normal man can support for a period of 
not over 1 minute, is 85 mgm. per cu m , according to Flury, and 
40-45 mgm per cu. m., according to Ferrarolo. 3 The mortality- 
product is 2,000 according to Miiller, and 4,000 for 10 minute's 
exposure according to Prentiss. 

5. Cyanogen Iodide. CNI (M.Wt. 153) 

Cyanogen iodide has a powerful lachrymatory action. It was 
prepared by Serullas in 1824. 4 It was not used as a war gas in 
the war of 1914-18 however. 

Preparation 

It is prepared by the action of iodine on mercuric cyanide 5 or 
sodium cyanide 6 

12 gm. iodine and 20 gm water are placed in a flask of about 
200 ml. capacity fitted with (1) a tap-funnel containing 100 ml. of 
a 5% aqueous solution of sodium cyanide, (2) an inlet tube for 
gas, and (3) an outlet tube. The contents of the flask are stirred 
and 50 ml. of the sodium cyanide solution are run in little by 
little with continued agitation. The sodium iodide formed in 
the reaction dissolves the iodine and the liquid in the flask is 
continuously decolourised. When the 50 ml. sodium cyanide 
solution have been added, a slow current of chlorine is passed into 

1 T Shimidzu, / Pharmac Soc Japan, 1926, 538, 107 

2 Pancenko, op cit 

3 Ferrarolo, Pohchmco (pract sect ), 1936, 1435 

4 Serullas, Ann chim phys , 1824, [2] 27, 188 

6 Seubert, Ber , 1890, 23, 1063 , R Cook, / Chem Soc , 1935, 1001 
• Nekrassov, op cit. 



CYANOGEN IODIDE 



195 



the flask, and while continuing to agitate the liquid the other 
50 ml. cyanide solution are added from the tap-funnel at such a 
rate that there is always an excess of iodine present. The current 
of chlorine is then stopped and a little more sodium cyanide is 
added. The reaction product is then extracted with ether, the 
ethereal extract dried over calcium chloride and the ether distilled 
off. A crystalline residue of cyanogen iodide remains. 
Yield 80-85% of theoretical. 

Physical and Chemical Properties 

Cyanogen iodide forms white crystals which gradually decom- 
pose, liberating iodine. 1 It melts at 146° C, according to Cook, 2 
and in a closed tube at 140 0 C. according to Zappi. 3 It dissolves 
sparingly in cold water but with ease in hot. It is more soluble 
in alcohol and ether. The vapour density is 5-3 (air = 1). 

Cyanogen iodide reacts with hydriodic acid much more readily 
than the chloride and bromide, iodine being liberated. 

Sulphurous acid is oxidised to sulphuric acid : 

2CNI + H 2 S0 3 + H 2 0 = H 2 S0 4 + 2HCN + I 2 
and sulphur is liberated from sulphides. 4 

It reacts quantitatively with sodium arsenite according to the 
equation 5 : 

CNI + Na 3 As0 3 + 2 NaOH = NaCN + Na 3 As0 4 + Nal + H 2 0. 

It also reacts with hydrochloric acid, forming iodine mono- 
chloride : 

CNI + HC1 = 2HCN + IC1, 
and with hydrobromic acid liberating bromine and iodine : 
2CNI + 2HBr = 2HCN + I 2 + Br 2 . 

It does not react with silver nitrate. On treatment of an 
aqueous solution of cyanogen iodide with potassium hydroxide 
and subsequent addition of ferrous and ferric salts and hydro- 
chloric acid, a precipitate of Prussian blue is obtained. 6 

The reactions of cyanogen iodide with many other substances 
have been studied. 7 From these it has been found that when 
treated with reducing agents its iodine is completely removed, 
while other reagents which normally remove iodine from iodides 
do not affect it. 

1 Seubert, Ber., 1890, 23, 1063. 

2 R. Cook, loc. ext. 

8 Zappi, Bull. soc. Mm., 1930, [4] 47, 453. 
4 A. Gutmann, Z. anal. Chem., 1925, 246. 

6 G. Alsterberg, Biochem. Z., 1926, 172, 223. 

• E. Zappi, Rev. fac. cienc. quim. Univ. La Plata, 1930, 7. 

7 Meyer, /. prakt. Chem., 1887, 35, 292. 

7-2 



196 



CYANOGEN DERIVATIVES 



6. Bromobenzyl Cyanide. (M.Wt. 196) 

/Br 

x Br 

Bromobenzyl cyanide was prepared by Reimer 1 in 1881, but 
it was not isolated in the pure state until 1914 .It was employed 
as a war gas by the French in the last years of the war, usually 
in solution in chloropicrin. 

According to American experiments made since the war, this 
compound is to be considered as one of the most efficient of the 
war gases because of its great persistence and its high lachrymatory 
power. 

It is also known as " Camite " (France), and by the symbol 
" CA " (America). 

Preparation 

Bromobenzyl cyanide was prepared by Reimer by the action of 
bromine on benzyl cyanide heated to 120° to 130° C. 

This compound may be prepared either by the action of 
cyanogen bromide on an alcoholic solution of benzyl cyanide in 
presence of sodium ethylate, according to the equation 2 : 

/Br 

C 6 H 6 CH 2 CN + BrCN + NaOC 2 H 5 = C 6 H 5 CH( + NaBr+C 2 H 5 OH 

N CN 

or else, by a method similar to that used by Reimer, by the action 
of bromine vapour on benzyl cyanide heated simply to 105° C, or 
to 120 0 C. while the gas mixture is exposed to the light of a 
1,000 c.p. Osram lamp. By this method a much higher yield of 
bromobenzyl cyanide is obtained. 3 

Laboratory Preparation 4 

In preparing this substance, it is advisable to start with 
benzyl bromide and first convert this into the cyanide, which is 
afterwards brominated. 

60 gm. benzyl bromide, 27 gm. potassium cyanide, 45 gm. 
ethyl alcohol and 25 gm. water are placed in a flask fitted with a 
reflux condenser and boiled for 4 hours. The mixture is then 
extracted with ether, the ether extract separated and dried over 
calcium chloride, the ether distilled off and the residue itself then 

1 Reimer, Ber , 1881, 14, 1797 , Steinkopf, Ber , 1920, 53, 1146 , Nekrassov, 
/ prakt Chem , 1928, 119, 108 

2 Von Braun, Ber , 1903, 36, 2651 

8 Steinkopf and coll , Ber , 1920, 53, 1144 
* Nekrassov, op cit 



BROMOBENZYL CYANIDE: PREPARATION 197 



distilled, the fraction boiling between 210 0 and 240° C. being 
collected. This may then be fractionally redistilled, when the 
portion boiling between 228 0 and 233° C. is collected. 

36 gm. benzyl cyanide are placed in a flask of 100-150 ml. 
capacity, fitted with a two-holed stopper. Through one of the 
holes a reflux condenser passes and through the other a tap- 
funnel. The top of the condenser is connected by means of a tube 
bent at right angles with a flask containing water which serves to 
absorb the hydrobromic acid evolved during the reaction. 

60 gm. bromine are added slowly from the tap-funnel during 
\ hour while the benzyl cyanide is heated to about 120° C. 
After allowing to cool, the product is washed with 5% soda 
solution, extracted with ether and the ether removed by distilla- 
tion, after filtering. The residue is then distilled in steam or at 
reduced pressure (25 mm.). 

Industrial Manufacture 1 

In the industrial manufacture of bromobenzyl cyanide it is 
preferable to commence with benzyl chloride rather than benzyl 
bromide. This is easily obtained by the chlorination of toluene 
under the influence of sunlight (see p. 129) or by the aid of a 
mercury vapour lamp. 2 

An alcoholic solution of benzyl chloride is heated at 80° C. for 
3-4 hours with the corresponding quantity of potassium or sodium 
cyanide dissolved in water : 



When the reaction is complete the alcohol is first distilled off and 
then the residue is distilled in a current of steam until no more 
oily distillate comes over. Crude benzyl cyanide is thus obtained. 
As the yield of bromobenzyl cyanide is greatly dependent on the 
purity of the benzyl cyanide, it is advisable to purify the latter 
by fractional distillation under reduced pressure. 

The benzyl cyanide obtained may be converted into bromo- 
benzyl cyanide by treatment with a mixture of air and bromine 
vapour in sunlight or under the influence of ultra-violet rays 3 : 



The amount of air should be carefully regulated so that bromine 
is neither carried forward nor remains in the benzyl cyanide as 
hydrobromic acid, this latter eventuality causing the formation 

1 Knoll, Synthetische und Isolierte Riechstoffe, Halle, 1928, 194. 

2 Mark and Wald, D.R.P. 142,939. 
8 Steinkopf, Ber., 1920, 53, 1146. 



C 6 H 5 — CH 2 C1 + KCN = KC1 + C 6 H 5 — CH 2 CN. 



C 6 H 6 -CH 2 CN + Br 2 = HBr + C 6 H 5 -CH< 




'CN 



CYANOGEN DERIVATIVES 



of a dibrominated derivative which has no aggressive properties. 
The reaction temperature is about 60° C. 

After the bromine has been completely absorbed, dry air is 
passed through the reaction-product to drive off any traces of 
hydrobromic acid. This is absorbed in sodium hydroxide and 
may be recovered. The bromobenzyl cyanide is stored in 
containers coated internally with lead, or enamelled. 

Physical and Chemical Properties 

Pure bromobenzyl cyanide forms yellowish-white crystals 
melting at 25-4° C. 1 In time these crystals become pink by 
incipient decomposition. 

The technical product is an oily liquid, brown with the 
impurities, usually liquids, which it contains. In order to purify 
it, it is necessary to recrystallise repeatedly from alcohol. It has 
a pungent but not disagreeable odour. 

The pure product boils at ordinary pressure at 242 0 C. with 
decomposition, distilling unaltered at 132° to 134° C. at 12 mm. 
mercury pressure. 

The specific gravity of bromobenzyl cyanide between 0° C. and 
50° C. is as follows : 

TEMPERATURE 

0 c. S - G ' 

o i-536o 

5 I-53I2 

10 1-5262 

20 1-5160 

30 1-5000 

50 1-4840 

The vapour tension of bromobenzyl cyanide is given in the 
following table at various temperatures -. 

TEMPERATURE VAPOUR TENSION 

0 C. MM. MERCURY 

o 0-0019 

IO 0-0050 

20 00120 

30 0-028I 

50 0-I280 

The vapour density is 6-8 (air = 1). The latent heat of 
volatilisation is 58-7 cals. The volatility at 20° C. is 130 mgm. 

1 Because of its high melting point, it has been proposed to employ bromobenzyl 
cyanide in solution 111 chloiopicnn. The melting points of such mixtures are as 
follows (Libermann) : 

100 parts bromobenzyl cyanide and 10 parts of chloropicnn, 9° C. 



BROMOBENZYL CYANIDE: PROPERTIES 199 

per cu. m. (Prentiss), and at 30° C. is 420 mgm. per cu. m. 1 
Miiller 2 reports a volatility of 750 mgm. per cu. m., which 
possibly refers to the technical product. 

It is insoluble in water, though it easily dissolves in many 
organic solvents (alcohol, benzene, carbon disulphide, acetic acid, 
acetone, ether, chloroform, carbon tetrachloride, etc.). It is also 
soluble in several of the other war gases, such as phosgene, 
chloropicrin, etc. Because of this property, it may be used 
together with these war gases so as to attain a more complete 
range of effects. 

Bromobenzyl cyanide decomposes on heating : at 160° C. the 
decomposition commences with the formation of dicyanostilbene 
and hydrobromic acid : 



It is highly resistant to chemical and atmospheric agencies. 
Water and humidity decompose it only very slowly. Cold 
sodium hydroxide solution acts similarly, though on prolonged 
boiling almost quantitative decomposition takes place with an 
aqueous solution of sodium hydroxide. A 20% solution of 
sodium hydroxide decomposes two and a half times its own weight 
of the cyanide. Alcoholic potash decomposes it even in the cold. 

When treated with some of the most vigorous oxidising agents, 
such as potassium or sodium chlorate, potassium permanganate, 
peroxides, etc., it is attacked only slowly. Owing to this stability 
to humidity and to chemical reagents, as well as its low vapour 
pressure, this substance has a high persistence, especially in 
suitable meteorological conditions such as cold, dry weather. 3 

Bromobenzyl cyanide in alcoholic solution reacts with sodium 
sulphide to form dicyanobenzyl sulphide : 



which forms yellow crystals with m.p. 150 0 to 152 0 C. It is 
insoluble in water, but soluble in the common organic solvents. 

On boiling bromobenzyl cyanide with an aqueous-alcoholic 
solution of sodium thiosulphate, the sodium salt of cyanobenzyl 
thiosulphuric acid is formed : 

C 6 H 6 CH(CN)Br + Na 2 S 2 0 3 = C 6 H 5 CH(CN)S 2 0 3 Na + NaBr. 

1 Ferri and Madesani, Giornale Medicina Militare, 1936, Part I. 

2 Muller, Militar Wochenblatt, 1931, 116, 113. 

3 Muller, loc. cit., p. 754. 




C 6 H 5 CHCN 




C 6 H 5 CHCN 




+ 2 NaBr 



200 



CYANOGEN DERIVATIVES 



This, on treatment with hydrochloric acid, gives cyanobenzyl 
mercaptan : 

2 C 6 H 8 CH(CN)S 2 C>3Na + 2 H 2 0 + 2 HC1 = 

= [C 6 H 5 CH(CN)SH] 2 + 2 NaCl + 2 H 2 S0 4 

which forms crystals melting at 101° C. It is insoluble in water, 
but soluble in alkalies and in the common organic solvents. 1 

On mixing an alcoholic solution of bromobenzyl cyanide with 
ammonium thiocyanate, cyanobenzyl thiocyanate is formed : 

C 6 H 6 CHBrCN + NH 4 SCN = C 6 H 5 CH(CN)SCN + NH 4 Br. 

This forms white crystals with m.p. 63° to 65° C, insoluble in 
water, but soluble in all the usual organic solvents with the 
exception of ligroin. It decomposes on heating to ioo° C. 2 

From the practical point of view, bromobenzyl cyanide has a 
great limitation in application because of its low stability to the 
shock of the bursting of the projectile. It can only be employed 
in bombs with a comparatively small bursting charge. 

It also has the inconvenient property of vigorously attacking 
all the common metals except lead, and in doing so its lachryma- 
tory properties are destroyed. Containers which are to be used 
for holding bromobenzyl cyanide must therefore be coated 
internally with lead or glass. 

It does not attack rubber. 

It is highly irritant. The minimum concentration which 
causes lachrymation is 0-3 mgm. per cu. m. of air according to 
Muller, and 0-2 mgm. per cu. m. of air according to Ferri. 3 The 
limit of insupportability is 30 mgm. per cu. m. (Muller) ; 5 mgm. 
per cu. m. (Ferri). Haber's toxicity product is 7,500. This value 
is considered too low by Ferri and Madesani, from experiments 
carried out on dogs and cavies. According to these observers, 
the toxic-suffocating power of bromobenzyl cyanide is insufficient 
to be of practical use. 

7. Phenyl Carbylamine Chloride (M.Wt. 175) 

/CI 
C 6 H-N=C< 

X C1 

This substance was prepared in 1874 by Sell and Zierold, and 
was employed as a war gas towards the middle of 1917 (in May) 
by the Germans. It was principally used in projectiles together 

1 Kretov, /. Rusk. Fis. Khim. Obsc, 1929, 61, 1975. 

2 Kretov, he. cit. 

s Ferri and Madesani, loc. cit. 



PHENYL CARBYLAMINE CHLORIDE 201 

with dichloroethyl sulphide in order to mask the odour of the 
latter. 

Phenyl carbylamine chloride is usually prepared by the 
chlorination of phenyl isothiocyanate 1 : 

/CI 

C 8 H 5 -N=C=S + 2 Cl 2 = C e H 5 -N=C< + SC1 2 

N C1 

Various methods have been employed for preparing phenyl 
isothiocyanate. It may be obtained, for instance, from carbon 
disulphide and aniline, which react to form thiocarbanilide in 
presence of alkali hydroxides : 

/NH-C 6 H 5 
CS 2 + 2 C 6 H 5 -NH 2 = H 2 S + S=C( 

X NH-C 6 H 5 

and this on heating with acid decomposes into aniline and phenyl 
isothiocyanate : 

/NH-C 6 H S 

S=C W r w "* C « H *- NH * + C 6 H 5 -N=C=S 
JN H-C 6 H. 5 

Another rather similar method is to treat carbon disulphide 
with aniline in presence of lime. Calcium phenyl dithiocarbamate 
is first formed, according to the equation : 

>,$ 



C 6 H 5 -NH-C( V 



2 CS 8 + 2 C 6 H r NH s + Ca(OH) 2 = 2 H 2 0 + ^Ca 

0/ 

C 6 H S -NH-C( V 

On treating this with an alkaline zinc chloride solution it 
decomposes with production of phenyl isothiocyanate : 

S 

(C 6 H 5 -NH-(:-S) 2 Ca -> Ca(SH) 2 + 2 C 6 H 5 -N=C=S 

This second method of preparation was employed by the Germans 
during the war. 

Laboratory Preparation 2 

In the laboratory, phenyl isothiocyanate is first prepared from 
aniline and carbon disulphide and the product then chlorinated. 

1 Sell and Zierold, Ber., 1874, 7, 1228. 

* Nekrassov, op. cit. ; Nef, Ann., 1892, 270, 274. 



202 



CYANOGEN DERIVATIVES 



40 gm. aniline, 50 gm. carbon disulphide, 50 gm. alcohol and 
10 gm. potassium hydroxide are heated to boiling on a water-bath 
for 2-3 hours in a flask of about 300-400 ml. capacity fitted with 
a reflux condenser. The condenser is then altered so as to make 
distillation possible, and the excess of carbon disulphide and 
alcohol removed by distillation. The residue is taken up with 
water, when crystals of thiocarbanilide separate. These are 
filtered off and washed with water. After drying, 30 gm. are 
weighed into a round-bottomed flask of 350-400 ml. capacity 
which is connected with a Liebig's condenser. 120 ml. hydro- 
chloric acid (S.G. 1-19) are added and the mixture rapidly 
distilled almost to dryness. The distillate is collected in a 
separatory funnel and then diluted with an equal volume of 
water. The oily layer of phenyl isothiocyanate which separates 
is dried with calcium chloride and distilled under reduced pressure. 

15 gm. of the phenyl isothiocyanate obtained are placed in a 
flask of 50-100 ml. capacity and dissolved in 20 gm. chloroform. 
The solution obtained is cooled with ice and water and saturated 
with chlorine for about 2 hours. The current of chlorine is 
stopped when the space over the liquid is coloured greenish-yellow. 
The chloroform is distilled off and the residue fractionally distilled 
by heating the flask with a naked flame. The fraction which 
passes over between 200 0 and 215° C. is collected and purified 
further by distillation under reduced pressure. The yield is 
80-90% of the theoretical. 

Industrial Manufacture 

The method used by the Germans consisted in preparing the 
phenyl isothiocyanate first from carbon disulphide, milk of lime 
and aniline and then chlorinating this. 

450 kgm. carbon disulphide are mixed with an excess of a 30% 
milk of lime in a large iron vessel and then about 560 kgm. 
aniline are added in small quantities during 1 hour. The mixture 
is agitated for about 24 hours at 25 0 C. Meanwhile 840 kgm. 
zinc chloride are dissolved in sufficient water to give a 50% 
solution and this mixed with 550 kgm. of a sodium hydroxide 
solution of 40 0 Be. The products of the reaction are added to 
this and the whole is then maintained at 30° to 40° C. By the 
action of the sodium zincate, phenyl isothiocyanate is formed 
and this may be separated from the other products of the reaction 
by steam distillation. 

600 kgm. of the phenyl isothiocyanate are placed in a vessel 
and a current of chlorine bubbled through it, maintaining the 
temperature at 0° C, until the specific gravity of the reaction 



PHENYL CARBYLAMINE CHLORIDE 203 



product reaches the value of 1-45 (about 24 hours). The sulphur 
chloride is separated by distillation, when the phenyl carbylamine 
chloride remains as a residue ; it is transferred to containers for 
storage. Yield 90%. 

Physical and Chemical Properties 

Phenyl carbylamine chloride is an oily liquid which is only 
slightly volatile. It is pale yellow in colour and has an onion-like 
odour. At ordinary pressure it boils at 208° to 210 0 C., 1 and at 
15 mm. pressure at 95 0 C. The specific gravity is 1-30 at 15 0 C, 
and the vapour density is 6-03. The coefficient of thermal 
expansion is 0-000895. The volatility at 20° C. is 2,100 mgm. 
per cu. m. It is insoluble in water, but soluble in chloroform, 
carbon tetrachloride and other organic solvents. 

Like the isonitriles, it has a strong tendency to react with 
various substances. For instance, it reacts quantitatively with 
hydrogen sulphide even at ordinary temperature, forming phenyl 
isothiocyanate : 

/CI H\ 

C 6 H 5 -N=C^ + = 2 HCl + C 6 H 5 -N=C=S 

CI H 

In contact with mild oxidising agents like mercuric oxide, 
silver oxide, etc., phenyl isocyanate is formed : 

/CI Agv 
C 6 H 5 -N=C< + >0 = 2 AgCl + C 6 H 6 -N=C=0 
N C1 Ag 7 

It is not hydrolysed by water at ordinary temperatures, but 
on heating to 100° C. in a closed tube it is decomposed with 
formation of diphenyl urea : 

/CI H\ 

C 6 H 6 -N=C< + )0 = C 6 H 6 -N=C=0 + 2 HCl 
N C1 H 

/OH 

C e H s -N=C=0 + H 2 0 = CO< 

N NH-C 6 H 5 

2 C0(° H /NH-C 6 H 6 
Wc 6 H 5 = H 2 0 + C0 2 + CO< nhCsHs 

On heating with aniline it reacts vigorously, forming triphenyl 
guanidine (Nef). 

1 Bly and coll., /. Am. Chem. Soc, 1922, 44, 2896. 



204 



CYANOGEN DERIVATIVES 



Phenyl carbylamine chloride, even when diffused in the air 
in the vapour state (at concentrations above 4%), produces with 
the Grignard reagent (see p. 248) a turbidity like that obtained 
with dichloroethyl sulphide (Hanslian). 

In contact with steel it decomposes slowly. 

Owing to its high boiling point it is classed as a very persistent 
war gas, but found only limited employment in the last war. 

The irritant power of phenyl carbylamine chloride is very 
great ; according to Miiller 3 mgm. are sufficient to produce 
irritation. The limit of insupportability is 30 mgm. per cu. m. of 
air. The mortality-product is 3,000 according to Miiller and 
5,000 for 10 minutes' exposure according to Prentiss. 

Analysis of the Cyanogen Compounds 

Detection of Hydrocyanic Acid 

Of the various methods proposed for the detection of 
hydrocyanic acid, the following are recommended : 

The Prussian Blue Reaction. On addition to an alkaline 
solution of hydrocyanic acid of a few ml. of ferrous sulphate 
solution and of ferric chloride solution, then shaking and warming, 
a blue precipitate of ferric ferrocyanide appears on acidification 
with hydrochloric acid. In presence of only a trace of hydrocyanic 
acid, only a greenish-blue colouration appears, due to the formation 
of a colloidal suspension of the ferric ferrocyanide. On standing 
(sometimes for as long as 12 hours) the suspension settles to blue 
floes, leaving the supernatant solution colourless. 

This reaction is specific for hydrocyanic acid and is quite 
sensitive, detecting 5 mgm. per cu. m. of air according to Kolthoff } 

The Prussian blue reaction may be rendered more convenient 
in use by employing a reaction paper. For this purpose 
Ganassini's 2 paper is strongly recommended. It is prepared by 
immersing a strip of filter paper, just before use, in a mixture of 
10 ml. 10% ferrous sulphate solution (containing a trace of 
ferric salt) and 20 ml. of an alkaline solution of Rochelle salt 
(30 gm. Rochelle salt, 10 gm. potassium hydroxide and 100 ml. 
water). This paper should be exposed first to the atmosphere 
containing hydrocyanic acid and then to hydrochloric vapour, 
when it becomes greenish-blue. 

The Ferric Thiocyanate Reaction. This test is carried out on a 
solution of the material to be examined ; if the sample is gaseous, 
a solution may be obtained by bubbling it through an alkaline 

1 Kolthoff, Z. anal. Chem., 1918, 57, 1. 

2 Ganassini, Bull. soc. Medico chtrurg. d% Pavta, 1910. 



HYDROCYANIC ACID: DETECTION 



solution. The solution is evaporated on the water-bath with a 
little ammonium sulphide and the residue is taken up in dilute 
hydrochloric acid, filtered, and the filtrate then treated with a 
few drops of a very dilute solution of ferric chloride. In the 
presence of hydrocyanic acid the liquid is coloured blood-red, or 
merely pink if only traces of hydrocyanic acid are present, owing 
to the formation of ferric thiocyanate. When a weak colouration 
is obtained, it may be rendered more distinct by adding a little 
ethyl ether to the solution ; the ferric thiocyanate then passes into 
the ether, producing a more intense colouration. 1 

Guignard's Sodium Picrate Paper. 2 Sodium picrate paper on 
exposure to gaseous hydrocyanic acid assumes a blood-red colour 
by the formation of sodium isopurpurate. 3 

These papers are prepared by immersing strips of filter paper 
first in a o-i% aqueous solution of sodium carbonate, allowing 
them to dry, and then immersing them in a o-i% aqueous picric 
acid solution. The Guignard reaction is sensitive (0-05 mgm. 
hydrocyanic acid gives a colouration in 12 hours), but not specific, 
for various reducing substances, as aldehydes, acetone, hydrogen 
sulphide and sulphur dioxide also respond to it. 

Benzidine Acetate Reaction. If a solution of benzidine acetate 
is added to a dilute solution of hydrocyanic acid in presence of 
copper acetate, an intense blue colouration is produced. This 
reaction, which was suggested by Pertusi and Gastaldi, 4 is more 
conveniently applied by means of papers prepared as follows 5 : 

Two separate solutions are prepared : 

(a) 2-86 gm. copper acetate in 1 litre of water. 

(b) 475 ml. of a solution of benzidine acetate, saturated at 
ordinary temperature, together with 525 ml. water. 

The two solutions are mixed in equal parts just before use and 
strips of filter paper are immersed in the mixture. The two 
solutions may be kept separately for a long period if stored in a 
dark place, but the mixture undergoes alteration in the course 
of about a fortnight. 6 

According to Smolczyk, 7 on exposing a benzidine acetate paper 
in an atmosphere containing o-oooi% by volume of hydrocyanic 
acid (i-i mgm. per cu. m. at 20 0 C), the change of colour to blue 
takes place in 1 minute. 

1 Jofinova, /. Obscei Khim., Ser. A., 1935, 5, 34. 

2 Guignard, Compt. rend., 1906, 142, 552 ; Jofinova, /. Obscei. Khim., Ser. A., 
1935. 5, 34. 

* Waller, Proc. Roy. Soc. Lond., 1910, 82, 574. 

4 Pertusi and Gastaldi, Chem. Zeitung., 1913. 37, 609. 

6 Sievert and Hermsdorf, Z. angew. Chem., 1921, 34, 3. 

* D. Kiss, Z. ges. Schiess-Sprengstoffw., 1930, 6, 262. 

7 Smolczyk, Die Gas-Maske, 1930, 32. 



206 



CYANOGEN DERIVATIVES 



Wieland's Method. This method of detecting hydrocyanic acid 
depends on the decolonisation of starch iodide by the substance : 

HCN + I a = HI + CNI. 

This reaction was employed by the Americans during the war 
and was carried out by passing the gas to be examined through 
a 2% solution of sodium bicarbonate containing starch solution 
and iodine. In the presence of hydrocyanic acid the solution is 
completely decolourised. The reaction is quite sensitive (8 mgm. 
per cu. m. of air), but is not specific for hydrocyanic acid 
(Guareschi). 

Quantitative Determination of Hydrocyanic Acid 

Hydrocyanic acid may be determined gravimetrically, 
volumetrically or colorimetrically. 

Gravimetric Methods, These methods are seldom employed 
because of their laborious nature. In any case, their use is 
advisable only when the quantity of hydrocyanic acid to be 
determined is not too small. Of these methods, the procedure of 
Rose is the most generally employed. 1 

In this the hydrocyanic acid is precipitated by silver nitrate 
from solutions slightly acidified with nitric acid (not more than 
2% nitric acid). The precipitate is filtered on a tared filter, 
washed, dried at ioo° C. and reweighed. Rose also described the 
alternative procedure of heating the precipitate to redness for 
about \ hour and weighing it as metallic silver. 

Volumetric Methods, (i) Liebig's Method* This depends on 
the fact that when a neutral or alkaline solution of an alkaline 
cyanide is treated with silver nitrate solution drop by drop, a white 
precipitate of silver cyanide forms as each drop enters the 
solution. This disappears on shaking because the silver cyanide 
dissolves in the excess of alkali cyanide to form an argento- 
cyanide : 

KCN + AgCN = Ag(CN) 2 K. 

When all the cyanide has been transformed into argento-cyanide, 
however, the first drop of silver solution in excess produces a 
turbidity caused by the decomposition of the double cyanide 
and formation of insoluble silver cyanide : 

Ag(CN) 2 K + AgN0 3 = 2 AgCN + KN0 3 . 

The total reaction is as follows : 

2KCN + AgN0 3 = KN0 3 + Ag(CN) 2 K. 

1 Rose, Z. anal. Chem., 1862, 199 ; or Grkgor, Z. anal. Chem., 1894, 33, 30. 
a Liebig, Ann., 1851, 77, 102. 



HYDROCYANIC ACID: DETERMINATION 207 



In order to carry out this determination, not more than o-i gm. 
free hydrocyanic acid is treated with a few ml. of sodium 
hydroxide solution and 0-5 gm. sodium bicarbonate and made up 
to a volume of 50 ml. with water. The titration is carried out 
with decinormal silver nitrate solution, shaking until finally a 
slight permanent opalescence remains. 

1 ml. N/10 AgN0 3 = 0-005404 gm. HCN. 

In order to detect the end-point with greater ease it is better 
to add a little sodium iodide to the solution. This reacts with the 
silver nitrate only when all the hydrocyanic acid has been 
converted into the double cyanide. 

(2) Fordos and Gelis's Method. The method suggested by 
Fordos and Gelis 1 depends on the reaction between hydrocyanic 
acid and iodine in presence of alkali bicarbonate, which has been 
mentioned already : 

HCN + I 2 = HI + CNI. 

The solution for examination should not contain more than 
0-05 gm. hydrocyanic acid. It is treated with a few ml. of sodium 
hydroxide solution and 0-5 gm. sodium bicarbonate, and is then 
titrated with a decinormal solution of iodine until a yellow colour 
persists. In this case it is unnecessary to use starch as indicator : 

1 ml. N/10 iodine solution = 0-001351 gm. HCN. 

Several analytical procedures have been based on this reaction, 
e.g., those of Seil, 2 Page, 3 etc. The following is especially suitable 
for the analysis of hydrocyanic acid used in the mixtures of gases 
used for disinfestation. 

About 200 ml. distilled water are placed in a 1 -litre Woulfe's 
bottle having two necks. One of these necks is fitted with a 
delivery tube reaching almost to the bottom of the bottle for the 
entry of the gas mixture, while the other is connected with an 
aspirator. 5 ml. 5% sodium bicarbonate solution, 5 ml. 1% starch 
solution and 10 ml. standard iodine solution are added to ths 
water in the bottle, the concentration of the iodine solution being 
chosen according to the amount of hydrocyanic acid presumed 
to be present in the gas. Usually, in analysing disinfestation 
mixtures, an iodine solution containing 0-94014 gm. of iodine per 
litre is employed, 10 ml. of this solution corresponding to o-ooi gm. 
hydrocyanic acid. 

1 Fordos and Gelis, /. prakt. Chem., 1853, 59, 255. 

* G. Seil, Ind. Eng. Chem., 1926, 18, 142. 

3 Page and Gloyns, /. Soc. Chem. Ind., 1936, 55, 209. 



2o8 



CYANOGEN DERIVATIVES 



By means of the aspirator, which is of about 5 litres capacity, 
the gas sample is drawn slowly through the Woulfe's bottle. 
The absorbing liquid is continually agitated. The water flowing 
out of the aspirator is accurately measured in a graduated 
cylinder. When the iodine solution is decolourised the gas-flow is 
immediately stopped and the water volume 
measured, this corresponding to the volume of 
gas examined. 

(3) Colorimetric Method. For the approxi- 
mate estimation of hydrocyanic acid in air, 
W. Deckert's 1 apparatus may be employed. 
This is based on the intensity of the blue 
colour produced by hydrocyanic acid on 
benzidine acetate paper (see p. 205). 

The apparatus consists of an aspirator A 
(see Fig. 13), one stroke of whose piston 
aspirates 25 ml. air through the aperture C. 
This air passes first through the cylinder B 
and then over the reaction paper which rests 
on the disc D. The disc is divided into three 
sectors coloured pale blue, blue and deep blue 
respectively. 

In carrying out an analysis with this 
apparatus, a sufficient number of inspirations 
of air are made to obtain a colouration of the 
reaction paper to match one of the three sectors. The amount of 
HCN in the air may then be obtained from the following : 

Pale blue corresponds to 0-004 mgm. HCN. 
Blue „ 0-008 

Deep blue „ 0-012 

This is accurate to ± 25%. 



8 





Quantitative Determination of Cyanogen Chloride 

Cyanogen chloride may be estimated by utilising its reaction 
with alkalies. 2 The substance to be examined is treated with an 
excess of a standard solution of sodium hydroxide and the 
excess then determined by titration with sulphuric acid. 
Phenolphthalein should be used as the indicator, as it does not 
react with sodium cyanate : 

CNC1 + 2NaOH = NaCNO + NaCl + H 2 0. 

1 W. Deckert, Z. Desinfekt. Gesundh., 1930, 22, 81. 
a Mauguin and Simon, Compt. rend., 1919, 169, 383. 



CYANOGEN COMPOUNDS : ANALYSIS 



From this equation it is seen that each molecule of cyanogen 
chloride reacts with two molecules of sodium hydroxide. If, for 
instance, N ml. normal sodium hydroxide were used and n ml. 
normal sulphuric acid were necessary to neutralise the excess, 
the quantity of cyanogen chloride present in the sample is given 
by the following : 

CNC1 = (N -n) 0-0306. 

Quantitative Determination of Cyanogen Bromide 

(1) The Hydriodic Acid Method. The determination of cyanogen 
bromide by this method depends on the estimation of the iodine 
liberated in the reaction between hydriodic acid and cyanogen 
bromide 1 : 

CNBr + 2HI = I, + HBr + HCN. 

In carrying out this determination, a weighed quantity of 
cyanogen bromide is treated with an excess of hydriodic acid 
solution, which is prepared by dissolving 10 gm. potassium iodide 
in 100 ml. of a 5% solution of acetic acid. The iodine liberated is 
titrated with a decinormal solution of sodium thiosulphate. 

(2) The Ammonia Method. This method depends on the 
decomposition of cyanogen bromide by ammonia : 

2NH3 + CNBr = NH 4 Br + NH 2 CN, 

and the titration of the ammonium bromide formed with silver 
nitrate. 2 

The sample to be analysed is weighed accurately into a flask, 
about 100 ml. aqueous ammonia are added and the flask stoppered 
and allowed to stand in the cold for about 20 minutes. After 
warming for a short time on the water-bath, the solution is 
diluted with 300 ml. water and brought to the boil to free it from 
the excess of ammonia. It is then slightly acidified with nitric 
acid and titrated with silver nitrate solution. 

The decomposition of cyanogen bromide may be carried out 
with sodium or potassium hydroxide instead of ammonia. 

Quantitative Determination of Cyanogen Iodide 

The determination of cyanogen iodide may be carried out 
by utilising its reaction with sodium arsenite 3 : 

CNI + NagAsOa + H 2 0 = HCN + HI + Na 3 As0 4 . 

1 Chattaway, /. Chem. Soc, 1902, 81, 196. 

2 F. Oberhauser and I. Schormuixer, Ber., 1929, 62, 1439. 
' Gutmann, Ber., 1909, 42, 3624 ; Z. anal. Chem., 1925. 246. 



210 



CYANOGEN DERIVATIVES 



The sample is treated with an exactly measured quantity of 
standard arsenious acid solution in excess and an excess of a 15% 
solution of sodium hydroxide. The liquid is warmed on the 
water-bath, and while still hot a slow current of carbon dioxide 
is passed through until the hydrocyanic acid is completely 
eliminated. The solution is then allowed to cool and made up to 
a convenient volume. The excess of arsenious acid is then 
determined in an aliquot of this by addition of sodium bicarbonate 
and titration with a standard solution of iodine. 



CHAPTER XIV 
SULPHUR COMPOUNDS 
(A) MERCAPTANS AND THEIR DERIVATIVES 

The mercaptans may be considered as derivatives of hydrogen 
sulphide, with one hydrogen atom substituted by an alkyl 
radical. 

These compounds, unlike hydrogen sulphide itself, have a 
comparatively low toxicity, confirming what has already been 
indicated regarding the influence of alkyl groups on the toxicity 
of substances. It also follows that the introduction of one or more 
halogen atoms into the molecule does not generally increase the 
toxicity, but decreases the chemical stability. 

Of the chloro-compounds, perchloromethyl mercaptan and its 
less chlorinated derivative, thiophosgene, have been used as war 
gases. Although the latter cannot be considered as a mercaptan, 
it is described in this chapter because of its close relationship to 
perchloromethyl mercaptan. 

1. Perchloromethyl Mercaptan (M.Wt. 185-91) 



This substance was employed by the French in September, 
1915, but with little success owing to its low offensive powers. 

It was prepared in 1873 by Rathke 1 and later by others, by the 
action of chlorine on carbon disulphide : 



The temperature of the reaction should not be allowed to rise 
above 50° C., otherwise more highly chlorinated compounds will 
be formed, especially in the presence of an excess of chlorine. 

Perchloromethyl mercaptan may also be obtained by the action 
of chlorine on methyl thiocyanate 2 or on thiophosgene. 3 




1 Rathke, Ann., 1873, 167, 195. 

4 Tames, /. Chem. Soc, 1887, 51, 268. 

» Klason, Ber., 1887, 20, 2381. 



212 



SULPHUR COMPOUNDS 



Laboratory Preparation 

In the laboratory, perchloromethyl mercaptan is easily prepared 
by the method recommended by Helfrich, 1 based on the reaction 
of chlorine with carbon disulphide. 

75 gm. carbon disulphide and 0-3 gm. iodine are placed in a 
flask of 200-300 ml. capacity fitted with a reflux condenser. 
While the flask is being externally cooled with water, a current 
of dry chlorine is passed in for several hours. In order to 
accelerate the reaction, it is as well to expose the contents of the 
flask to diffused daylight. When the volume of the liquid has 
been approximately doubled (and its weight has reached about 
150-160 gm.) the current of chlorine is stopped and the mixture 
allowed to stand overnight. It is then warmed on the water-bath 
to drive off the excess of carbon disulphide and also the carbon 
tetrachloride, which is formed as a secondary product of the 
reaction. The sulphur chloride is decomposed by adding an equal 
volume of water to the residue and shaking vigorously. This is 
then distilled first in steam and then under reduced pressure 
(50 mm.). 

Physical and Chemical Properties 

Perchloromethyl mercaptan is an oily, clear yellow liquid with 
an unpleasant odour, which boils at ordinary pressure at 148° to 
149° C. with decomposition. At 50 mm. pressure it distils 
unaltered at 73° C. Its specific gravity is 1722 at 0° C, its 
vapour density is 6-414, and its volatility is 18,000 mgm. per 
cu. m. at 20 0 C. 

When perchloromethyl mercaptan is heated with water in a 
closed tube to 160° C, it decomposes into carbon dioxide, 
hydrochloric acid and sulphur. 2 This decomposition also takes 
place to a very limited extent by the action of atmospheric 
humidity. 

In the presence of oxidising agents, the sulphur atom is 
oxidised and the perchloromethyl mercaptan is converted into 
trichloromethyl sulphonic chloride, CC1 3 — S0 2 — CI. 

Reducing agents act on perchloromethyl mercaptan in various 
ways. For instance, nascent hydrogen (from zinc and hydro- 
chloric acid) reduces it to methane, iron and hydrochloric acid 
converts it into carbon tetrachloride (Helfrich), while with 
stannous chloride, thiophosgene is obtained. 

1 Helfrich, /. Am. Chem. Soc, 1921, 43, 591 ; Autenrieth, Ber., 1925, 58, 
2152. 

» Rathke, Ann., 1873, 167, 201. 



THIOPHOSGENE 



213 



/CCI3 /CI 
S< + SnCl 2 = SnCl 4 + S=C< 
N C1 N C1 

This last reaction also takes place with some other reducing agents, 
such as copper and silver powder. 

When treated in the cold with chlorine, perchloromethyl 
mercaptan is converted into sulphur chloride and carbon 
tetrachloride 1 : 

/CCI3 

s( + Cl 2 = SCI, + CC1 4 

In contact with iron, perchloromethyl mercaptan decomposes 
even at ordinary temperatures. 2 

Perchloromethyl mercaptan has an irritant action on the 
eyes. The minimum concentration capable of causing this 
irritation is 10 mgm. per cu. m. of air. The limit of insupportability 
is 70 mgm. per cu. m. and the mortality-product is 3,000 (Muller). 

2. Thiophosgene (M.Wt. 114-98) 

S = o/ 
Vi 

Thiophosgene was prepared by Kolbe in 1843, 3 and was 
employed as a war gas by the Austrians and the French in the war 
of 1914-18 (" Lacrimite "). 

Preparation 

It may be obtained by passing a mixture of carbon tetrachloride 
and hydrogen sulphide through a red-hot tube, or by passing 
perchloromethyl mercaptan over silver powder 4 : 

CC1 4 S + 2Ag = CC1 2 S + 2AgCl. 

In the laboratory, it is preferable to prepare thiophosgene by 
the reduction of perchloromethyl mercaptan with tin and 
hydrochloric acid. 6 

60 gm. of granulated tin and 200 ml. hydrochloric acid (density 
1-19) are placed in a round-bottomed flask of about 1 litre 
capacity fitted with a tap-funnel and a reflux condenser. It is 
warmed gently to accelerate solution of the tin and meanwhile 
60-70 gm. perchloromethyl mercaptan are added gradually 

1 James, /. Chem. Soc, 1887, 51, 273. 

8 Frankland and coll., /. Soc. Chem. Ind., 1920, 39, 256. 

3 Kolbe, Ann., 1843, 45, 44. 

4 Rathke, Ann., 1873, 167, 204. 
6 Klason, Ber., 1887, 20, 2380. 



214 



SULPHUR COMPOUNDS 



from the tap-funnel. When it has all been added the contents of 
the flask are heated and the thiophosgene distilled off. In order 
to obtain a purer product it is redistilled. 

In France during the war, thiophosgene was prepared by acting 
on carbon disulphide with chlorine at ordinary temperatures and 
then reducing the perchloromethyl mercaptan formed as 
intermediate product with stannous chloride. 

Physical and Chemical Properties 

Thiophosgene is an oily liquid with an orange-yellow colour 
and a pungent odour. It fumes in the air and boils at 73-5° C. 
Its specific gravity at 15 0 C. is 1-508 and its vapour density 4. 
It is insoluble in water. On heating even to 200° C, it decomposes 
to a slight extent (Klason), but on heating with dry ammonium 
chloride it is quantitatively decomposed into carbon disulphide 
and carbon tetrachloride 1 : 



Exposure to light, even for a short time, converts it into a 
polymer of the formula C 2 C1 4 S 2 . This is termed " dithiophosgene " 
and forms colourless crystals melting at 116° C. 2 

Water slowly decomposes thiophosgene in the cold and 
rapidly hot (Bergreen) : 



A similar decomposition is produced by the action of alkalies. 
With ammonia, ammonium thiocyanate is formed. The alkali 
sulphites react vigorously as follows (Rathke) : 

/CI 



Chlorine is rapidly absorbed even in the cold, perchloromethyl 
mercaptan being formed (Klason). 

Strong acids, even fuming nitric acid, do not decompose it (Kolbe) . 

The lethal concentration for 30 minutes' exposure is 4,000 mgm. 
per cu. m. of air (Lindemann). 

(B) SULPHIDES (THIOETHERS) AND THEIR DERIVATIVES 

The sulphides, or thioethers, whose general formula is R — S — R, 
may be considered as derivatives of hydrogen sulphide in which 

1 Bergreen, Ber., 1888, 21, 339. 

» G.Carrara, Atti accad. Lined., 1893, 1, 421 ; Rathke, Ber., 1888, 21, 2539. 




•ci 



/CI 

S=C^ + 2 H 2 0 = H 2 S + 2 HC1 + C0 2 




THE SULPHIDES 



215 



both the hydrogen atoms have been substituted by alkyl 
groups. 

These compounds have no toxic action on the human organism, 
but, like the sulphur derivatives already described, a certain 
degree of toxicity and in some cases powerful vesicant power are 
acquired when one or more of the hydrogen atoms in the alkyl 
radicals are substituted by one or more halogen atoms. Thus 
from methyl sulphide, chloromethyl sulphide is obtained, this 
having a toxic power on the respiratory system. From ethyl 
sulphide, derivatives are obtained which have differing toxic 
actions according to whether the halogen atom is attached at 
position a or /? : 

/CH 2 -CH 3 
S \ 

CH 2 -CH 3 



The monosubstituted derivatives, ethyl /? chloroethyl sulphide 
and ethyl jS bromoethyl sulphide, 1 are weak in toxicity, as is also 
the disubstituted compound aa' dichloroethyl sulphide. 2 The 
disubstituted derivative with both the halogen atoms in the /? 
position, )8j8' dichloroethyl sulphide, however, is powerfully toxic 
and vesicant : it is more commonly known as " Mustard Gas." 

Other derivatives analogous to /?/?' dichloroethyl sulphide have 
been prepared, such as #8' dibromoethyl sulphide 3 and #8' 
diiodoethyl sulphide, 4 which have similar physiopathological 
properties, as well as homologues of dichloroethyl sulphide 
such as j8j8' dichloropropyl sulphide (I) and #9' dichlorobutyl 
sulphide (II) : 

CH 3 

/CH 2 -CHC1-CH 3 /(!:H-CHC1-CH 3 
X CH 2 -CHC1-CH 3 X CH-CHC1-CH 3 

c:h 3 

I II 

These two substances resemble /?/?' dichloroethyl sulphide in 
odour, but show some differences in offensive action, for it has 
been found that only /?/?' dichlorobutyl sulphide possesses vesicant 
action and that to a much milder degree than the ethyl compound. 5 

1 Steinkopf, Ber,, 1920, 53, 1007. 

2 Bales, /. Chem. Soc, 1922, 121, 2137. 
8 Steinkopf, Ber., 1920, 53, 1011. 

* Helfrich and Reid, /. Am. Chem. Soc., 1920, 42, 1219. 

« Pope, /. Chem. Soc, 1921, 119, 396 ; Coffey, /. Chem. Soc, 1921, 119, 94. 



2l6 



SULPHUR COMPOUNDS 



Derivatives have also been prepared with the chlorine atom 
in the y position, like yy dichloropropyl sulphide, whose toxic 
properties are, however, as yet unknown, 1 and also derivatives 
with chlorine atoms in the /? and y positions, such as ffiyy 
tetrachloropropyl sulphide : 

/CH,-CHC1-CH 2 C1 
S< 

N CH 2 -CHC1-CH 2 C1 

whose physiopathological properties are similar to those of 
dichloroethyl sulphide, but not so vigorous. 2 

Attempts made to prepare substances like 88' dichlorobutyl 
sulphide with chlorine atoms in the 8 position have not been 
successful up to the present. 

With regard to the relations between the chemical structure of 
these substances and their vesicant power, the following 
observations may be made : 

(a) Of the halogenated sulphides prepared and studied only 
those with the halogen atoms at the end of the carbon chain have 
vesicant properties. 

(b) The CH 2 -group in the a position should remain unsubstituted. 
It has been shown that on substituting a hydrogen atom in this 
group with a halogen atom, as in a$8' trichloroethyl sulphide (I) , 
or replacing each pair of hydrogen atoms in the two CH 2 -groups 
with oxygen, as in monochloroacetic thioanhydride (II) : 

/CHCl-CH a Cl /CO-CH 2 Cl 
S< S( 
N CH 2 -CH 2 C1 N CO-CH 2 Cl 

I II 

the products are completely or almost completely deprived of 
vesicant properties. 

(c) The introduction of one or more sulphur atoms linked with 
one or more CH 2 -groups, between the chloroethyl groups, as in 
dichloroethyl ethylene dithioglycol 3 : 

S-CH 2 -CH 2 C1 

CH a 

CH 2 

CH 2 — CH 2 C1 



A- 



1 Bennett, /. Chem. Soc, 1925, 127, 2671. 

2 E. Boggio-Lera, Chim. e Industria, 1935, 334. 

3 Bennett, /. Chem. Soc, 1921, 119, i860 ; Rosen, /. Am. Chem. Soc, 1922, 
44, 634. 



DICHLOROETHYL SULPHIDE: INTRODUCTION 217 



diminishes the vesicant power, but confers orticant properties 
(see p. 147). 

Of the analogues of dichloroethyl sulphide, the following have a 
place in the chemistry of the war gases : 

(a) $8' dichloroethyl selenide, 1 crystals melting at 24-2° C., 2 
which have a vesicant action on the skin like that of the 
corresponding sulphide but to a less degree. This action is 
produced by a benzene solution of dichloroethyl selenide 
containing more than 2% as selenium. 3 

(b) Dichloroethyl telluride, which, according to American 
experiments, does not possess the interesting offensive properties 
expected of it (Hanslian). 

1. Dichloroethyl Sulphide (Mustard Gas) (M.Wt. 159) 

/CHo — CHoCl 

CHg — CH2CI 

The discovery of this war gas, more commonly known as 
" Iprite " from the locality (Ypres in Flanders) where it was first 
used, is due to Despretz, 4 who obtained it in 1822 by the reaction 
of ethylene on sulphur chloride. 

It is also known as " Senfgas," " Mustard Gas " (England), 
" Ypirite " (France) and " Lost " (Germany). This last name is 
derived by joining the first letters of the names of the two 
Germans, Lommel and Steinkopf, who proposed and studied the 
use of this gas in warfare. In America, it is refered to in the 
Chemical Warfare Service as " HS." 

The application of this substance as a war gas, which commenced 
in July 1917 by the Germans, marked the beginning of a new 
period of chemical warfare and constituted a great surprise for 
the Allied armies. It was identified a few days after it was first 
used, but its preparation on an industrial scale required several 
months of study and research by the Allies. By the end of the 
war, however, the potential production of the Allied plants was 
greater than that of the German. 

Preparation 

After Despretz, this substance was prepared by Riche 5 in 
1854, and later by Guthrie 6 in i860, while studying the condensa- 

1 H. Bausor and coll., /. Chem. Soc, 1920, 117, 1453 I C. Boord, /. Am. 
Chem. Soc, 1922, 44, 395 ; Poggi, Gazz. chim. Ital., 1934. 64> 497. 
8 H. Bell and coll., /. Chem. Soc, 1925, 127, 1877. 

3 G. Ferrarolo, Pensiero Medico, 1936, No. 5. 

4 Despretz, Ann. chim. phys., 1822, [2] 21, 428. 
6 Riche, Ann. chim. phys., 1854, [3] 42, 283. 

• Guthrie, Quart. Jour. Chem. Soc, i860, 12, 116. 



2i8 



SULPHUR COMPOUNDS 



tion products of the halogens and of the halogenated sulphur 
compounds with the olefines. Guthrie, to whom many accounts 
have erroneously attributed the discovery of dichloroethyl 
sulphide, prepared it like Despretz by bubbling ethylene through 
sulphur chloride and noticed its peculiar vesicant properties. 

At the same time, but independently of Guthrie's work, 
Niemann, 1 in i860, employing the same method as Despretz, 
obtained dichloroethyl sulphide, but was not able to determine 
its chemical constitution. 

Later, in 1886, Meyer 2 made a special study of the compound 
and succeeded in preparing it in the pure state by a completely 
new process depending on the chlorination of thiodiglycol with 
phosphorus trichloride, and described its physical, chemical and 
biological properties. 

More recently, in 1912, Clarke 8 prepared this compound by a 
method similar to that of Meyer, that is, by chlorination of 
thiodiglycol, but used hydrochloric acid instead of phosphorus 
trichloride. 

In 1920, Gibson and Pope 4 perfected Guthrie's method by. 
bubbling dry and completely alcohol-free ethylene through 
sulphur dichloride maintained in agitation at 40 0 to 45 0 C. : 

/CI /CH 2 CH 2 C1 
2CH 2 =CH 2 + S( S< 

N C1 X CH 2 CH 2 C1 

By employing sulphur monochloride instead of the dichloride, 
the reaction passes through the following phases, according to 
Conant 5 : 

S 2 C1 2 ?± S + SC1 2 
/CI 

CH 2 =CH 2 + SC1 2 ->S( 

CH 2 CH 2 C1 

/CI /CH 2 CH 2 C1 
CH 2 =CH 2 + S< -> S< 

N:h 2 ch 2 ci n ch 2 ch 2 ci 



Furthermore, the following secondary reaction takes place : 



/CI ^ /CH 2 CH 2 C1 

-»\ "4* nS = S n \ -f- S 2 Cl 2 



CH 2 CH 2 C1 N CH 2 CH 2 C1 

1 Niemann, Ann., i860, 113, 288. 

2 V. Meyer, Ber., 1886, 19, 632, 3259. 

3 Clarke, /. Chem. Soc, 1912, 101, 1583. 

* Gibson and Pope, /. Chem. Soc, 1920, 117, 271. 
5 Conant and coll., /. Am. Chem. Soc, 1920, 42, 585. 



DICHLOROETHYL SULPHIDE : PREPARATION 219 



Other methods of preparing dichloroethyl sulphide of minor 
importance have been proposed : 

Steinkopf's method, 1 which consists in reacting on a solution of 
thiodiglycol in chloroform with thionyl chloride also dissolved in 
chloroform : 



/CH 2 CH 2 OH /CH 2 CH 2 C1 
S< 4 SOC1, = S< + S0 2 + H 2 0 

N CH 2 CH 2 OH N CH 2 CH 2 C1 

Myers and Stephen's method? in which a mixture of 75 parts of 
sulphur dichloride and 25 parts of sulphur monochloride is 
sprayed in an atmosphere of ethylene. According to the authors, 
this method permits the rapid and continuous preparation of 
dichloroethyl sulphide in 93% yield, without over-chlorination. 

Laboratory Preparation 

Dichloroethyl sulphide may be easily prepared in the laboratory 
by following Guthrie's original method : bubbling ethylene 
through sulphur chloride. 

An apparatus like that shown in Fig. 14 is set up. The reaction 




111 



Fig. 14. 

between the ethylene and the sulphur chloride takes place in the 
Woulfe's bottle A (capacity 100-200 ml.) which has three necks, 
one of which serves to carry off excess gas, another is fitted with 
a tap-funnel B in which the sulphur chloride is placed, while 
ethylene, made in the flask C, is introduced through the third. 
The three wash-bottles contain respectively (I) concentrated 
sulphuric acid, (II) 10% sodium hydroxide and (777) concentrated 

1 Steinkopf, Ber., 1920, 53, 1007. 

1 Myers and Stephen, /. Soc. Chem. Ind., 1920, 39, 656T. 



220 



SULPHUR COMPOUNDS 



sulphuric acid, and serve to dry the ethylene. It is advisable 
not to connect the wash-bottle III to the Woulfe's bottle until 
the evolution of the ethylene has become regular. 

25 gm. alum and a mixture of 25 gm. ethyl alcohol and 150 gm. 
concentrated sulphuric acid (density 1-84) are placed in the 
flask C, which is then heated cautiously. As soon as the current 
of ethylene becomes steady, wash-bottle III is connected with the 
Woulfe's bottle, in which 20 gm. sulphur chloride have been 
previously placed. At the same time a mixture of 150 gm. ethyl 
alcohol and 300 gm. concentrated sulphuric acid is introduced 
drop by drop into C from the tap-funnel D. 

During the passage of the ethylene, a further 30 gm. sulphur 
chloride are added from the tap-funnel B in three portions and 
the Woulfe's bottle is immersed in a vessel containing water so 
that the temperature of the reaction mixture does not exceed 
35° C. The passage of the ethylene through the Woulfe's bottle 
is continued until all the sulphur chloride has been used up. This 
stage is determined by treating a little of the product with 
sodium iodide solution. 

At the end of the reaction the product is distilled under reduced 
pressure, the fraction passing over between 106° and 108° C. at 
15 mm. pressure being collected. 

Industrial Manufacture 

Dichloroethyl sulphide may be prepared industrially by several 
processes, all of which are based on one of the two methods 
described above : Meyer's and Guthrie's. 

The various stages of manufacture by Meyer's process, which is 
referred to as " the German process," as it was largely employed 
during the war of 1914-18 by Germany, may be schematically 
expressed as follows : 



(a) Preparation of Ethylene : 

C 2 H 5 OH = H 2 0 + CH 2 = CH 2 . 

(b) Preparation of Ethylene Chlorohydrin : 

Ca(C10) 2 + H 2 0 + C0 2 = CaC0 3 + 2HCIO 
CH 2 = CH 2 + HC10 = Cl.CH 2 .CH 2 .OH 

(c) Preparation of Thiodiglycol : 



OH-CHa-CHg-Cl 
OH-CHj-CH-i-a 



+ 




S = 2 NaCl -f S' 




DICHLOROETHYL SULPHIDE: MANUFACTURE 221 



[d) Preparation of Dichloroethyl Sulphide : 

/CH 2 -CH 2 -OH /CH 2 -CH 3 C1 
S< 4 2 HC1 = 2 H 2 0 + S< 

x CH 2 -CH 2 -OH N CH a -CH 2 Cl 

Guthrie's method, which was used by 'the Allies, and is, 
therefore, referred to as " the Allied process," consists simply in 
acting on sulphur chloride with ethylene : 

/CH 2 -CH S C1 
2 CH 2 =CH 2 4- SClg = S( 

2 2 N CH 2 -CH 2 C1 

/CHa-CHjCl 

or else : 2 CH 2 =CH 2 + S 2 C1 2 = S< t S 

N CH 2 -CH 2 C1 

Meyer's Method : Preparation of Ethylene. Ethylene is 
prepared by passing ethyl alcohol in the vapour state over 
aluminium oxide heated to 350 0 to 400 0 C. The dehydration 
reaction is as follows : 

C 2 H s OH = C 2 H 4 + H 2 0. 

The alcohol is first vaporized by passing it through coils 
heated to 8o° to 90 0 C. and through a copper tube containing the 
catalyst and heated in a bath of fused potassium nitrate. The 
reaction products then pass through coolers where the water and 
alcohol are condensed while the ethylene is washed and led into 
storage vessels. 

Preparation of Ethylene Chlorohydrin. 1 This reaction is carried 
out in large cylindrical iron pans, lined with lead and coated 
externally with cork. 5 cu. m. (1,100 gallons) of water and 
bleaching powder equivalent to 500 kgm. active chlorine are 
placed in this vessel and while stirring well a current of carbon 
dioxide is introduced in order to liberate part of the hypochlorous 
acid. After about 20 minutes, ethylene instead of carbon dioxide 
is introduced to saturation point and finally carbon dioxide and 
ethylene simultaneously until all the hypochlorite has reacted. 
The reaction should be carried out at as low a temperature as 
possible, between 5° and 10° C, the reaction mixture being 
cooled by circulating a cooling mixture through coils. 

After the ethylene has been absorbed, the reaction products 
are pumped through a filter-press to remove the calcium carbonate 
and the filtrate, which contains from 10 to 12% ethylene 

1 G. BozzA and Mamoli, Giorn. chim. ind. applicata., 1930, 283. 



222 



SULPHUR COMPOUNDS 



chlorohydrin, is distilled in steam so as to obtain a solution 
containing 18-20% of the chlorohydrin. 1 

Preparation of Thiodiglycol. The theoretical quantity of 
sodium sulphide is added to the chlorohydrin solution, prepared 
as already described, and the mixture heated to about 90° to 
100° C, the product being drawn over into an evaporator and 
again heated to remove all the water. The thiodiglycol formed is 
filtered, and distilled in vacuo. 

Note. According to Nenitzescu, 2 the preparation of 
thiodiglycol may be carried out by acting on ethylene oxide with 
hydrogen sulphide at 40° to 60° C. in presence of a small quantity 
of thiodiglycol which acts as a solvent for the two gases. 



This method gives a yield of 90%. 

Preparation of Dichloroethyl Sulphide. The chlorination of 
thiodiglycol is carried out in cylindrical cast-iron pans, 2*5 m. in 
height and 2-8 m. in diameter, lead-lined and jacketed so that the 
reaction mass may be heated and cooled. The hydrochloric acid 
necessary for the chlorination is first passed through sulphuric 
acid and then introduced into the thiodiglycol as slowly as possible 
so as to obtain complete absorption. During the reaction the 
temperature is held at about 50 0 C. Two layers form in the pan, 
a heavy oily one consisting of a solution of dichloroethyl sulphide 
in thiodiglycol and an upper one consisting of an aqueous solution 
of hydrochloric acid. At the end of the reaction, the oily layer 
is drawn over into a lead-lined iron vessel fitted with lead coils 
for heating and a condenser, also constructed of lead, connected 
to a vacuum pump. The water is removed by distillation under 
reduced pressure (60-70 mm.) and the residual liquid then 
treated in a mixer with suitable solvents. 

Guthrie's Method [the Allied Process). This method, compara- 
tively simple for preparing small quantities of dichloroethyl 
sulphide in the laboratory, presented considerable technical 
difficulties when first used on the industrial scale. These were 
later overcome by the efforts of English and American 
chemists. 3 

Compared with the Meyer process, the Guthrie method allows 

1 M. Gomberg, /. Am. Chem. Soc, 1919, 41, 1414. 

2 Nenitzescu, Antigaz, 1935, 9, No. 9, 12 ; No. 11, 3. 

» A. Green, /. Soc. Chem. Ind., 1919, 38, 363, 469 ; Gibson and Pope, /. Chem. 
Soc, 1920, 117, 271. 




D1CHL0R0ETHYL SULPHIDE 



the product to be prepared more rapidly and in better yield, 
but it requires careful control during the course of the 
reaction. 1 

Several systems of manufacture were proposed and actually 
employed during the war for the preparation of dichloroethyl 
sulphide by this process. 2 The most successful procedure in 
practice was that of Levinstein which was first used in America 
and then later by the Allies. 

The preparation of dichloroethyl sulphide by this method was 
carried out in a cylindrical vessel of sheet steel or cast-iron, 
lead-lined and jacketed, of about 100 cm. diameter and 130 cm. 
in height, fitted with an agitator. This vessel has a lid through 
which a pipe passes to within a short distance of the bottom in 
order to introduce the ethylene. 

Sufficient sulphur monochloride to cover the end of the tube 
is first placed in the vessel and then ethylene is bubbled in, so 
arranging the speed of its introduction and the cooling that the 
temperature of the reaction mixture remains at 30 0 to 35 0 C. 
Meanwhile more sulphur monochloride is added in small portions. 
Employing 430 kgm. of ethylene, which needs 750 kgm. sulphur 
chloride, the reaction is completed in about 20 hours. At the end 
of the reaction the product is siphoned into a settling vessel 
where the sulphur is removed. 

Physical Properties 

In the pure state, dichloroethyl sulphide is an oily, colourless 
liquid which boils at 760 mm. pressure at 217-5° C. 3 and melts 
at 14-4° C. 4 In the crude state, it is brown and has a characteristic 
odour which is reminiscent of mustard. The melting point of the 
crude product is lower than that of the pure substance and varies 
with the impurities present. 

The latent heat of fusion is 25 calories, the refractive index n D 
is 1-53125 (Pope and Gibson), and the coefficient of thermal 

1 Report of the Chemical Warfare Service of January 16th, 1918 (Jackson, 
Chem. Rev., 1934, 4 26 )- 

* For detailed descriptions of the French method (Pascal), see Giua, Chimica 
degli aggressivi chimici, Turin, 1931. 68 ff. 

8 This value is that quoted by Meyer; other authors, like Vedder and Hanslian, 
however, give the boiling point of dichloroethyl sulphide as 219-5° C. This 
discordance may be attributed to the fact that this substance decomposes at its 
boiling point at ordinary pressure. According to Flury and Wieland the boiling 
point at 15 mm. mercury pressure is 108° to io9°C, and according to Clarke 
(/. Chem. Soc., 1912, 101, 1583) 97° to 98° C. at a pressure of 10 mm. 

* In the literature many different values are quoted for the melting point of 
dichloroethyl sulphide : Meyer (1887), 12° C. ; Gibson and Pope (1919), 13° to 
I 3-5° C. ; Gomberg (1919), 14-5° C. ; Delepine and Flury (1920), 14° to 14-5° C. ; 
Fries (1921), 13 0 to 14° C. The most dependable value is 14-4° C. for the pure 
substance. 



224 



SULPHUR COMPOUNDS 



expansion 0-000881. The specific gravity of the solid is 1-362 
at 9 0 C. (Vedder) and 1-338 at 13 0 C. (Fries). 

The specific gravity of liquid dichloroethyl sulphide and the 
corresponding specific volume are given in the following table at 
various temperatures 1 : 



TEMPERATURE 

(°c) 


SPECIFIC GRAVITY 


SPECIFIC VOLUME 


15 


I-2790 


0-78l 


20 


I-274I 


0-785 


25 


1-2686 


0-788 


30 


1-2635 


0-79I 


35 


1-2584 


0-795 


40 


1-2531 


0-798 


50 


1-2426 




75 


1-2158 




90 


1-1996 





The vapour density of dichloroethyl sulphide in the gaseous 
state, calculated by dividing the weight of a litre of the vapour 
(7-09 gm.) by the weight of a litre of air (1-293 gm.), is 5-4. 

The vapour pressure of dichloroethyl sulphide at various 
temperatures may be calculated from the formula (see p. 11) : 

2734-5 

log p = 8-3937 — 



The values of the vapour pressure determined experimentally 
and calculated from the formula already quoted 2 are given in 
the following table, as well as the corresponding values for the 
volatility 3 at various temperatures : 



TEMPERATURE 

°c. 


vapour tension (mm. mercury) 


volatility 

mgm. /litre 


Obs. 


Calc. 


0 


0 035 


0-024 


0-28 


10 


0-055 


0-054 




15 


0-075 


0-079 


0-401 


20 


0-115 


0-115 


0-625 


25 






0-958 


30 


0-225 


023 


1-443 


35 






2-135 


40 


o-45 


o-45 


3-66 


50 


0-83 


0-85 




60 


i-55 


1-52 





1 Wilkinson and Wernlund, /. Am. Chem. Soc, 

2 Mumford and coll., /. Chem. Soc., 1932, 589. 

3 Vedder, loc. cit. 



1920, 42, 1382. 



DICHLOROETHYL SULPHIDE 225 



The values of the vapour tension and of the corresponding 
volatilities of dichloroethyl sulphide in the solid state are, 
according to Vedder : 



TEMPERATURE 


VAPOUR TENSION 


VOLATILITY 


°C. 


mm. mercury 


mgm.j litre 


— 17-8 


OOO45 


0-045 


O 


OO31 


0-28 



Because of its low vapour tension, dichloroethyl sulphide 
evaporates very slowly, in spite of its low specific heat (0-330 
calories) and low latent heat of volatilisation (80 calories). It is 
thus highly persistent, especially on terrain covered with bushes 
and shrubs (see p. 12). 

Dichloroethyl sulphide is very sparingly soluble in water, its 
solubility increasing to a certain limit with increase in tempera- 
ture. According to Hopkins 1 the solubility in water is 0-033% 
at o-6° C, and 0-07% at io° C. According to French data, 2 the 
solubility at 25 0 C. is 0-047%, an< ^ according to American data 3 
0-069%. 

It is, however, very soluble in various hydrocarbons 4 and 
organic solvents, such as kerosene (in which it is soluble in all 
proportions at 26° C), petrol, carbon tetrachloride, mono- 
chlorobenzene, ethyl alcohol (in absolute alcohol it is soluble in 
all proportions above 15-6° C., and above 38-6° C. in 92-5% 
alcohol), 6 ethyl ether, carbon disulphide, thiodiglycol, glycerol, 
as well as in the animal and vegetable oils and fats. It is only 
slightly soluble in vaseline and paraffin wax. 6 

Dichloroethyl sulphide also dissolves in chloropicrin. 7 It is 
absorbed by rubber and penetrates leather and the ordinary 
textile fabrics. 

The following observations have been made on the degree of 
penetration of dichloroethyl sulphide into various materials 8 : 

Into ordinary brickwork, very little penetratjion ; increased if 
the material is very porous. 

1 Hopkins, /. Pharmacol., 1919, 12, 393. 

2 Boulin and Simon, Compt. rend., 1920, 170, 845. 

3 Wilson, /. Am. Chem. Soc, 1922, 44, 2867. 

* Thompson and H. Odeen, /. Ind. Eng. Chem., 1920, 12, 1057. 
6 Thompson and Black, /. Am. Chem. Soc, 1921, 43, 877. 

6 Schroter, Drager-Hefte, 1936, No. 186, 3309. 

7 Lindemann, Yperit, Warsaw, 1929, 74. 

* Themme, Gasschutz und Luftschutz, 1936, 189, also considers the penetration 
of dichloroethyl sulphide into bitumen, tar, linoleum, road-making materials, etc 

WAR GASES. 8 



226 



SULPHUR COMPOUNDS 



Into glazed brickwork and porcelain it does not penetrate, but 
spreads out slightly, remaining thus until it has completely 
evaporated. 

Oil paints applied to house walls offer protection to penetration 
provided that the paint coating is homogeneous and free from 
cracks. 

Unpainted woodwork easily absorbs dichloroethyl sulphide, 
penetration into the fibres taking place very easily along the 
grain. 

The action of dichloroethyl sulphide on parchment, documents, 
seals, deed papers, handwriting, etc., has also been studied. On 
these objects dichloroethyl sulphide in the vapour form has been 
applied without having any noticeable action, though in the 
liquid state it penetrates paper, shellac, wax, etc. 1 

Chemical Properties 

At ordinary temperature, dichloroethyl sulphide is a stable 
compound, but on heating it decomposes into hydrochloric acid 
and toxic and lachrymatory gases whose composition has not yet 
been denned. This decomposition commences at about 150° C. 
and is complete at 500 0 C. 

According to Bell, 2 on heating dichloroethyl sulphide at 180° C. 
for 18 hours, dithiane and ethylene dichloride are formed : 

/CH,CH,C1 /CH 2 CH A 
2 S( — S( )S + 2 C 2 H 4 C1 2 

CH 2 CH 2 C1 CH 2 CH 2 

This reaction is reversible, so that on heating dithiane with 
ethylene dichloride to 180° C. dichloroethyl sulphide is formed. 

Dichloroethyl sulphide in contact with water undergoes 
hydrolysis even at ordinary temperatures to form thiodiglycol 
and hydrochloric acid : 



Thiodiglycol 3 is a colourless, syrupy liquid with a characteristic 
odour, soluble in water, ethyl alcohol, acetone and chloroform, 
but sparingly soluble in ether, benzene and carbon tetrachloride. 
On heating at ordinary pressure it decomposes without distilling. 
At 12 mm. of mercury pressure it distils at 161° to 165 0 C, and 




HOH 



HOH 




1 Zernick, Archiv. Zeitschr., 1936, 44, 185. 

2 Bell and coll., /, Chem. Soc, 1927, 1803. 

3 Gomberg, /. Am. Chem. Soc, 1919, 41, 1414. 



DICHLOROETHYL SULPHIDE 



at 2 mm. of mercury it distils at 130° C. Its specific gravity at 
20° C. is 1-1821. 

As to the velocity of hydrolysis of dichloroethyl sulphide, a 
subject not without a certain interest, especially from the military 
point of view, there is not the least information in pre-war 
literature. Thefirst studies commencedini.918-19 with Hopkins's 1 
work, and were continued with those of Rona 2 and of Wilson. 3 

These have shown that complete hydrolysis of dichloroethyl 
sulphide takes place by an irreversible reaction 4 except in the 
presence of a considerable quantity of hydrochloric acid. The 
velocity of the hydrolysis may be determined either by measuring 
the development of acidity or of the quantity of ionised chlorine 
present (Hopkins), or from the decrease in electrical resistance. 
This velocity is influenced by various factors, such as the time 
of contact, the temperature, the water /dichloroethyl sulphide 
ratio, the quantities of acid, alkali and hydrolysis products 
present, as well as the degree of dispersion of the dichloroethyl 
sulphide in the water. 

In the following table, due to Hopkins, the degree of hydrolysis 
at the ordinary temperature (20° to 2i°C.) is given as a function 
of the time of contact of the dichloroethyl sulphide with water : 

% DICHLOROETHYL SULPHIDE 
TIME HYDROLYSED COMPARED WITH 

minutes that dissolved 

IO 50 
20 70 

30 79 

40 84 

50 85 

60 85 

Regarding the influence of the ratio of water to dichloroethyl 
sulphide, it has been found that in presence of a large excess of 

1 Hopkins, / Pharmacol , 1919, 12, 393, 403 

2 Rona, Z ges expt Med , 1921, 13, 16, also gives the velocity of hydrolysis of 
substances similar to dichloroethyl sulphide, like tetrachloroethyl sulphide, 
dibromoethyl sulphide, etc 

3 Wilson, / Am. Chem Soc , 1922, 44, 2867-2878 

4 According to the experiments of Wilson (loc at ) and Peters and Walker 
(Btochem J , 1923, 17, 260) the hydrolysis of dichloroethyl sulphide takes place 
m two distinct steps, one reversible and the other irreversible 

<CH,CH,C1 /CH,CH 2 C1 
4 HOH «± S( + HC1 

CH.CH.Cl X^CH.OH 

/CH,CH,C1 /CHjCHjOH 

(ii) s< + hoh = s< + hc1 

Yh 3 ch 2 oh Vh,ch s oh 

8—2 



228 



SULPHUR COMPOUNDS 



water the conversion into thiodiglycol is practically quantitative 
according to the equation already given. 1 

If, however, the amount of water is small compared with that 
of the dichloroethyl sulphide, for instance three times the volume 
of the sulphide, only a little thiodiglycol is formed, together with 
hydrochloric acid and a complex mixture of sulphonium chlorides, 
some of which form dichloroethyl sulphide with concentrated 
hydrochloric acid, while others do not. These latter compounds 
are formed principally when the ratio of water to the sulphide is 
very small. The only one which has been isolated is the following 
compound 1 : 



As to the influence on the hydrolysis of the degree of dispersion 
of the dichloroethyl sulphide, Wilson's 2 experiments have shown 
that the hydrolysis is considerably accelerated by adding alkaline 
solutions of sulphonated vegetable or animal oils, for example, 
solutions containing 3% of sulphonated corn oil and 2% sodium 
carbonate. These have the effect of increasing the degree of 
dispersion of the substance. 

Reactions of Dichloroethyl Sulphide in which the Sulphur 
Atom takes part 

With Oxidising Agents, Like all thioethers, dichloroethyl 
sulphide tends to add one or two oxygen atoms and be converted 
into the corresponding sulphoxide or sulphone by oxidising agents 
like nitric acid, hydrogen peroxide, potassium permanganate, 
chromic acid, etc. 



Dichloroethyl sulphoxide may be obtained, according to Gibson 
and Pope, 3 by placing a drop of dichloroethyl sulphide in 
concentrated nitric acid (d. 1-40) at ordinary temperature. 
The reaction is violent, heat is evolved and a bright green liquid 
is formed. When this liquid is diluted with water, a white 




'CH a CH 2 \ /CH 2 CH 2 OH 
CH 2 CH/ n C1 





dichloroethyl sulphoxide 



dichloroethyl sulphone 



1 Davies and Oxford, /. Chem. Soc, 1931, 224. 

a Wilson, /. Am. Chem. Soc, 1922, 44, 2762. 

8 Gibson and Pope, /. Chem. Soc., 1920, 117, 271. 



DICHLOROETHYL SULPHIDE 



precipitate of the sulphoxide separates. On crystallising this 
from 60% alcohol, colourless scales are formed which melt at 
110° C. This substance is soluble in water (1-2 gm. in 100 ml. 
at 20°C), in alcohol (4-3 gm. in 100 ml. at 20°C), in ether, 
benzene, carbon disulphide, acetone, chloroform and mineral 
acids. 1 On distilling even at reduced pressure it partly decomposes 
and the principal product of the decomposition is dichloroethyl 
sulphide. 

Dichloroethyl sulphoxide has also been prepared by Steinkopf 2 
from the reaction of hydrogen peroxide on dichloroethyl 
sulphide. 

According to Marshall and Williams, 3 this substance has no 
vesicant action on the skin. 

Dichloroethyl sulphone may be obtained by the oxidation 
of dichloroethyl sulphoxide or sulphide. Thus by the action of 
potassium permanganate on dichloroethyl sulphide, Steinkopf 4 
obtained the sulphone as colourless crystals melting at 52 0 C. 6 
and boiling at 179° to 181 0 C. at 14-15 mm. of mercury pressure. 
This compound is sparingly soluble in water (o-6 gm. in 100 ml. 
at 20° C, and 2-4 gm. in 100 ml. at 100° C.) and is only slightly 
hydrolysed. It is soluble in alcohol (7-1 gm. in 100 ml. at 20° C), 
ether, chloroform, etc. Helfrich and Reid obtained the sulphone 
by treating the sulphoxide in the cold with a solution of chromic 
acid in sulphuric acid. 

According to Marshall, the sulphone in contact with the skin 
produces vesicles and persistent ulcers. Its vapour has a 
lachrymatory and sometimes even a sternutatory action. This 
physiopathological action is not observed when working with the 
substance at ordinary temperatures because of its low vapour 
pressure. 

By the action of the strongest oxidising agents, 6 such as fuming 

1 Helfrich and Reid, /. Am. Chem. Soc, 1920, 42, 1208. 

2 Dichloroethyl sulphoxide may be prepared as follows, according to Steinkopf 
(Ber., 1920, 53, 1007) : 23 gm. 30% hydrogen peroxide are added slowly to a 
cooled solution of 32 gm. dichloroethyl sulphide in 100 ml. acetic acid. The 
reaction is violent and heat is developed. After cooling and allowing to stand, 
the sulphoxide deposits when the solution is diluted with water. 

3 Marshall and Williams, /. Am. Chem. Soc, 1920, 42, 1298. 

4 Preparation of the sulphone, according to Steinkopf (Ber., 1920, 53, 1007) : 
20 gm. dichloroethyl sulphide, dissolved in 100 ml. of an aqueous solution of 
acetic acid (1 : 1), are shaken with a saturated aqueous solution of 30 gm. 
potassium permanganate in presence of 20 ml. dilute sulphuric acid, and then 
allowed to stand. After reduction of the excess permanganate with sulphur 
dioxide, crystals of the sulphone separate. 

6 According to Helfrich (loc. cit.), the melting point of this substance is 
56 0 C. and its boiling point 183 0 C. at 20 mm. pressure. 

• Bennett, /. Chem. Soc, 1921, 119, 418; 1922, 121, 2139; Mann and 
Pope, /. Chem. Soc, 1922, 121, 594. 



230 



SULPHUR COMPOUNDS 



nitric acid, on heating or in a closed tube at 100° C, dichloroethyl 
sulphide is converted into /? chloroethane sulphonic acid : 



and by the action of aqua regia it is converted into sulphuric acid 
and carbon dioxide. 

With Chlorine. Lawson and Dawson 1 obtained a compound 
of the following structure : 



by bubbling a current of chlorine through a solution of dichloro- 
ethyl sulphide in carbon tetrachloride cooled to — 5 0 C. This 
forms white needles, unstable at ordinary temperatures (see 

P- 234)- 

With Bromine. Bromine also reacts easily with dichloroethyl 
sulphide. According to Gibson and Pope, 2 on treating a cold 
solution of dichloroethyl sulphide in chloroform with bromine 
an unstable addition compound is obtained. This is orange-yellow 
and has the following structure : 

(C1CH 2 — CH^gS.aBrj. 

It decomposes to form a less highly brominated substance : 

(C1CH 2 — CH 2 ) 2 S.Br 2 . 

which is obtained as a yellow powder, m.p. 43° to 44° C. Sodium 
hydroxide solution converts it into dichloroethyl sulphoxide. 

With Iodine. According to Lindemann 3 a tetraiodo derivative 
is obtained, " tetraiodo-iprite " : 



With Fluorine. No additive compounds of fluorine and 
dichloroethyl sulphide have been mentioned in the literature. 
With Sulphur Chloride. From the reaction between sulphur 

1 Lawson and Dawson, /. Am. Chem. Soc, 1927, 49, 3119. 

2 Gibson and Pope, /. Chem. Soc, 1920, 117, 271, 
a Lindemann, Yperit, Warsaw, 1929, 47. 





€H 2 -CH 2 C1 
'CH 2 -CH 2 C1 




>CH 2 -CH 2 -1 
CH 8 -CHj-I 



DICHLOROETHYL SULPHIDE 



monochloride and dichloroethyl sulphide, a compound of the 
following formula is obtained 1 : 



that is, the same substance which is obtained from the action of 
chlorine on dichloroethyl sulphide. It forms white needles and 
is unstable at ordinary temperatures (see p. 234). 

With Bleaching Powder. Dry chloride of lime reacts with 
dichloroethyl sulphide, acting as oxidant and chlorinating agent. 2 
A very violent reaction, with evolution of heat, flame and white 
vapours, takes place. Numerous compounds are formed : carbon 
dioxide, hydrochloric acid, chloroform, chloral and chlorinated 
substances which are not yet defined. 3 

According to some workers, dichloroethyl sulphoxide is also 
formed in this reaction 4 : 



The temperature of the reaction rises to such a point that 
combustible material (hay, paper, etc.) is inflamed. 

By the action of chloride of lime mixed with water the action 
is less violent. 

Bleaching powder is used to decontaminate objects which 
have been contaminated with mustard gas. For this purpose it is 
recommended that the bleaching powder be mixed to a porridge 
with water, or with some other powdered substance, so as to 
prevent the inconvenient results already mentioned, which would 
be caused by the violence of the reaction. In the reaction with 
undiluted bleaching powder, a zone of contact forms, consisting 
of a layer of decomposition products which protects the sulphide 
from further attack. 5 

Chloride of lime may also be employed for decontamination of 
the skin. In this case the violence of the reaction should be 
reduced by mixing the bleaching powder with water (1 part of 
water to 1 part of chloride of lime) or with magnesium oxide. 8 

1 LlBERMANN, Op. cit. 

2 Wirth, Gasschutz und Luftschutz, 1932, 2, 60. 

8 Desgrez and coll., Chim. ei Ind., 1921, 6, 842. With regard to the practical 
aspects of decontamination with chloride of lime, see Drager, Gasschutz im 
Luftschutz, Lubeck, 1934, 98 • 

4 Meyer, Der Gaskampf und die chemischen Kampfstoffe, Leipzig, 1925, 406. 

* Renwanz, Die Gasmaske, 1935, 1. 

« Muntsch, Eathologie und Therapie der Kampfgaserkrankungen, Leipzig, 1935. 




< 



<CH 2 CH 2 C1 
CH 2 CH 2 C1 



-f- CaOCL, = OS( 



>CH 2 CH 2 C1 
'CH 2 CH 2 C1 



+ CaCl 2 



232 



SULPHUR COMPOUNDS 



The decontaminating power of the bleaching powder depends 
on the content of active chlorine. According to Weidner, 1 in 
order to obtain sufficient decontaminating action, the bleaching 
powder should contain at least 15% active chlorine. 

With Sodium Hypochlorite. On bubbling a current of carbon 
dioxide through a mixture of dichloroethyl sulphide and sodium 
hypochlorite solution, oca'/?/?' tetrachloroethyl sulphoxide 2 is 
formed : 

/CHC1-CH 2 C1 
OS( 

N CHC1-CH 2 C1 

This is a crystalline substance melting at 121° C. 

With Iodine Trichloride. On adding a carbon tetrachloride 
solution of dichloroethyl sulphide to a solution of iodine trichloride 
also in carbon tetrachloride, an addition compound of the 
following formula is immediately formed 3 : 

/CH 2 CH 2 C1 



CI/ N CH 2 CH 2 C1 

In the presence of an excess of iodine trichloride or of iodine 
trichloride and free chlorine, dissolved in carbon tetrachloride, 
dichloroethyl sulphide is converted into a yellow crystalline 
substance of the formula : 

I\ /CH 2 CHoCl 

X 

CI/ N CH 2 CH 2 C1 

This reaction may be used for the detection of dichloroethyl 
sulphide. 

With Chloramine-T. Dichloroethyl sulphide reacts readily 
with chloramine-T (the sodium salt of ^-toluene sulphochloro- 
amide, CH 3 — C 6 H 4 — S0 2 — Na=NCl) to form an additive com- 
pound of the formula : 

/CH 2 -CH 2 C1 
CH 3 -CH 4 -S0 2 -N=S( 

N CH 2 -CH 2 C1 

which contains a tetravalent sulphur atom. The =S=N — 
according to Mann and Pope 4 may be termed the " sulphilimine " 
group. The condensation of dichloroethyl sulphide with 

1 Weidner, Gasschutz und Luftschutz, 1936, 133. 

2 Muller, J.prakt. Chem., 1926, 114, 123. 

* E. Boggio-Lera, Chim. e Industria, 1935, 334. 
4 Mann and Pope, /. Chem. Soc, 1922, 121, 1053. 



DICHLOROETHYL SULPHIDE 



233 



chloramine-T takes place even in the cold ; on adding 17-1 gm. 
dichloroethyl sulphide to an aqueous solution of 28 gm. 
chloramine-T, small white crystals separate after about an hour. 
They melt at 144-6° C. 

Chloramine-T is employed as decontaminating agent for 
dichloroethyl sulphide and has the advantage over bleaching 
powder of not producing too violent a reaction. Moreover, it is 
not toxic, non-irritant and keeps for a long time. It is recom- 
mended for the decontamination of clothing of linen, cambric, 
cotton and mixed fabrics. In decontaminating woollen materials 
it is necessary to avoid boiling. 1 

With Selenious Acid. Dichloroethyl sulphide reacts with 
selenious acid, reducing it to selenium : 



/ 

H 2 Se0 3 + S( 



CH 2 — CH 2 C1 
CHo — CHoCl 



A 



CH Q — CHoCl 



H 2 — CH 2 C1 



+ H 2 0 + Se 



The selenium separates in the form of an orange-yellow 
suspension. Selenious acid in sulphuric acid solution has been 
proposed by Yablich as a reaction for the detection of dichloroethyl 
sulphide (see p. 247). 

Reactions of Dichloroethyl Sulphide Involving the 
Whole Molecule 
With Chlorine. The behaviour of dichloroethyl sulphide with 
chlorine was studied by Mann and Pope 2 in 1922, by Lawson and 
Dawson 3 in 1927, by Mumford 4 in 1928, and by Phillips 5 in 
1929. 

By the action of chlorine on dichloroethyl sulphide at ordinary 
temperatures, the following compounds are obtained, according 
to Mann and Pope : 





S.G. 


B 

15 mm. 


p. 

mercury 


Trichloro-compound 


c/CHCl- 
^\CH a - 


-CILjCl 
-CH 2 C1 


I-42I9 


106° 


to 


108° C. 


Tetrachloro-compound 


c/CHCl- 
b \CH 2 - 


-CHCljj 
-CH 2 C1 


1 -5441 


123° 


to 


125° C. 


Hexachloro-compound 


c/CCl 2 — CC1 3 
S \CH 2 CH 2 C1 


1-6944 


160° 


to 


161 0 C. 



1 Weidner, he. cit. 

2 Mann and Pope, /. Chem. Soc., 1922, 121, 594. 

3 Lawson and Dawson, /. Am. Chem. Soc. 1927, 49, 31 19. 
* Mumford and Cole-Philips, /. Chem. Soc, 1928, 155. 

6 Phillips and Davies, /. Chem. Soc, 1929, 535. 



234 



SULPHUR COMPOUNDS 



These three chloro-derivatives are obtained as colourless liquids 
which become faintly green on exposure to daylight. They 
have odours similar to that of dichloroethyl sulphide, but have 
no vesicant properties, while their melting points are much lower. 

On examining these chloro-derivatives it was found that with 
the increase in the number of atoms of chlorine in their molecules, 
the tendency of the sulphur atom to pass from the divalent to the 
tetravalent condition diminished. 

Lawson and Dawson have observed that the first product 
formed in the chlorination of dichloroethyl sulphide is an additive 
compound containing tetravalent sulphur : 

/CH 2 -CH 2 C1 
Cl 2 • S< 

N CH 2 -CH 2 C1 

This compound is not very stable and is largely converted into 
a/?/?' trichloroethyl sulphide according to the equation : 

/CHg-CHjCl /CHC1-CHX1 
Cl 2 • S< -> S< + HC1 

N CH a -CH 2 Cl N CH 2 -CH 2 C1 

A small proportion decomposes into dichloroethyl sulphoxide and 
hydrochloric acid : 



ci 2 • s( 



CH 2 -CH 2 C1 + H 2 0 /CH 2 -CH 2 C1 

>» OS( + 2 HC1 

CH 2 -CH 2 C1 N CH 2 -CH 2 C1 



The trichloroethyl sulphide, according to Lawson, is itself not 
very stable and loses another molecule of hydrochloric acid to form 
a vinyl compound which can exist in two isomeric forms : 

/CC1=CH 2 /CH=CHC1 

N CH 2 -CH 2 C1 N CH 2 -CH 2 C1 

a-chlorovinyl jS-chlorovinyl 
jS-chloroethyl sulphide /3-chloroethyl sulphide 

Each of these contains only two chlorine atoms, like dichloroethyl 
sulphide. Neither possesses vesicant properties equal to that of 
j8j|8' dichloroethyl sulphide however (Dawson and Lawson). 

Later experiments on the action of chlorine on dichloroethyl 
sulphide have demonstrated that the chlorination is not limited 
to one chain of the molecule, but can take place in both the 
chloroethyl groups, and the following compounds have been 
prepared 1 : 

1 Phillips and Davies, loc. cit. 



DICHLOROETHYL SULPHIDE 



(a) aa/Ja'/?' pentachloroethyl sulphide, 

/CCVCHaCl 
^CHC1-CH 2 C1 

a mobile colourless liquid with density 1-57 at 20 0 C. 

(b) oaoc'/W hexachloroethyl sulphide. 



a colourless liquid boiling at 159 0 C. at 15 mm. mercury pressure 
and having a density of 1-6841 at 20 0 C. 
(c) oax'PPp'P' heptachloroethyl sulphide, 



a liquid boiling at 170 0 to 172 0 C. at 15 mm. of mercury, with a 
density of 17473 at 20 0 C. 

With Sulphur Chloride. The action of sulphur chloride on 
dichloroethyl sulphide has been studied by Gibson, 1 Mann and 
Pope. 2 It has been shown that the result of the reaction between 
these two compounds is different according to whether the 
sulphide reacts with sulphur monochloride or with sulphur 
dichloride. 

Sulphur monochloride reacts very slowly with $8' dichloroethyl 
sulphide in absence of catalysts, though in presence of iron the 
reaction is more lively. The products of the reaction are in each 
case hydrochloric acid, sulphur and a liquid consisting of 
trichloro- and tetrachloro-ethyl sulphides. 

Sulphur dichloride on the contrary reacts vigorously with 
dichloroethyl sulphide even at 0° C. The reaction may become 
violent according to the ratio of dichloroethyl sulphide to sulphur 
dichloride and heat is always developed. The products vary 
according to the relative quantities of the two reactants. If 
the dichloroethyl sulphide is in excess, the compound 
CI— S— CH 2 — CH 2 — CI is formed : 



S' 



>CC1 2 -CH 2 C1 
CHC1-CHC1 2 




'CH 2 CH 2 C1 
CH 2 CH 2 C1 



+ SC1 2 = 2 I 



CH 2 -C1 

c:h 2 -s-ci 



1 Gibson and Pope, /. Chem. Soc, 1920, 117, 271. 
1 Mann and Pope, /. Chem. Soc, 1922, 121, 594. 



236 



SULPHUR COMPOUNDS 



while if the sulphur dichloride is in excess, sulphur monochloride, 
hydrochloric acid and a trichloro-derivative are formed : 

/CH 2 -CH a Cl /CHC1-CH 2 C1 
2 SCl a + S< = S 2 C1 2 + HC1 + S< 

N CH 2 -CH 2 C1 N CH 2 -CH 2 C1 

With Hydriodic Acid. By the action of hydriodic acid in 
aqueous or acetic acid solution on dichloroethyl sulphide, both the 
chlorine atoms are substituted by iodine atoms and diiodoethyl 
sulphide is obtained (see p. 244). 

/CH 2 -CH 2 C1 /CH 2 -CH 2 I 

+ 2 HI = +2 HC1 

CJ^— CH 2 C1 CH 2 — CH 2 I 

Grignard's method for the detection of dichloroethyl sulphide 
depends on the reaction with sodium iodide (see p. 248). 

With the Alkali Sulphides. Sodium and potassium sulphides 
react readily with dichloroethyl sulphide to form diethylene 
disulphide, also termed " dithiane." 



< 



CH S -CH 2 \ 
/S 

CH^— CH 2 



This forms white crystals with a melting point of 112° C, and 
has no toxic power. It boils at ii5*6° C. at 60 mm. mercury 
pressure, 1 and is volatile in steam. It is sparingly soluble in 
water, but readily in alcohol and ether. This compound, which 
was first obtained by Meyer 2 in 1886, is converted into the 
corresponding disulphone by treatment with hydrogen peroxide 
in acetic acid solution 3 : 

/CH 2 — CH 2 \ 



o 2 s( 



)so 2 

CH 2 — CH 2 



Diethylene disulphide is also obtained, together with ^-thioxane, 

CH 2 CH 2 

by distilling thiodiglycol with potassium bisulphate. 4 It is also 
formed by the action of a saturated solution of hydrobromic 
acid in phenol on thiodiglycol. 5 

1 J. Johnson, /. Chem. Soc, 1933, 1530. 

1 Meyer, Ber., 1886, 19, 3259. 

s Fromm and Ungae, Ber., 1923, 56, 2286. 

* Fromm, Ber., 1923, 56, 2286. 

* E. Bell and coll., /. Chem. Soc, 1927, 1803. 



DICHLOROETHYL SULPHIDE 



Sodium disulphide in aqueous solution reacts slowly with 
dichloroethyl sulphide, forming 1 : 

S— CHo— CHo\ 

I )s 

S— CHjg-CHj 

ethylene trisulphide, crystals melting at 74° C. 

With Potassium Hydroxide, (a) In Alcoholic Solution. By the 
action of a 20% solution of potassium hydroxide in alcohol, 
dichloroethyl sulphide is converted into divinyl sulphide 2 : 

/CH=CH, 

N CH=CH 2 

a mobile liquid with a characteristic odour which boils at 85° to 
86° C. Its density at 15° C. is 0-9174. It readily polymerises, 
being transformed in less than a week into an opaque mass, 
soluble in carbon disulphide. 3 

Divinyl sulphide is also formed by the abstraction of two 
molecules of water from one of thiodiglycol. 4 On treatment 
with gaseous hydrochloric acid, it forms oca' dichloroethyl 
sulphide, 5 a colourless liquid with a penetrating odour, which 
boils at 58-5° C. at 15 mm. mercury and has a density of 1-1972 
at 15° C. On treatment of divinyl sulphide in aqueous solution 
with hydriodic acid, 6 /?/?' diiodoethyl sulphide is formed (see p. 244). 
With chlorine various chlorinated compounds are formed, for 
instance, a/? dichloroethyl vinyl sulphide : 

/CHC1-CH 2 C1 
N CH=CH 2 

and <x/?a'/?' tetrachloroethyl sulphide : 

/CHCl-CHjCl 
X CHC1-CH 2 C1 

Divinyl sulphide is formed quantitatively according to 
Helfrich 7 when dichloroethyl sulphide is treated with sodium 
ethylate. 

1 Fromm, Ber., 1925, 58, 304. 

a S. H. Bales and A. S. Nickelson, /. Chem. Soc, 1922, 121, 2137 ; 1923. 123, 
2486. 

s L. Lewin, /. prakt. Chem., 1930, 127, 77. 

4 E. Fromm and Ungar, Ber., 1923, 56, 2286. 

6 S. H. Bales and A. S. Nickelson, loc. cit. 

* J. Alexander and McCombie, /. Chem. Soc, 1931, 1913. 

» Helfrich and Reid, /. Am. Chem. Soc., 1920, 42, 1219, 1224. 



238 



SULPHUR COMPOUNDS 



By the action of a 50% solution of potassium hydroxide in 
alcohol other products besides divinyl sulphide are formed, 
probably its polymers. 

(6) In Aqueous-alcoholic Solution. By the action of a 20% 
solution of potassium hydroxide in aqueous alcohol on dichloro- 
ethyl sulphide, in the proportion of 1 part of the sulphide to 
4 parts of potassium hydroxide, the following compounds 1 are' 
formed, besides divinyl sulphide : 

Vinyl ft ethoxyethyl sulphide, 

/CH 2 -CH 2 OC 2 H s 
N CH=CH 2 

a mobile colourless liquid with a pungent odour resembling that 
of camphor. It boils at 65 0 C. at 8 mm. mercury pressure. Its 
density at 15° C. is 0-9532. 
/? ethoxy /?' hydroxyethyl sulphide 

/CH 2 CH 2 OC 2 H 5 
S< 

N CH 2 CH 2 OH 

a liquid boiling at 117-5° C. at 4 mm. mercury pressure. 
$8' diethoxy ethyl sulphide 

s ^CH 2 CH 2 OC 2 H 5 
CH 2 CH 2 OC 2 H 5 

a liquid boiling at 225° C. at 746 mm. mercury, with a density at 
20° C. of 0-9672. 

By varying the proportions of potassium hydroxide and 
dichloroethyl sulphide, various other compounds are formed, 
among them vinyl /? chloroethyl sulphide, 2 

/CHjCI^Cl 

x:h=ch 2 

a liquid boiling at 71° to 72° C. at 50 mm. mercury, which absorbs 
hydrochloric acid to form a/?' dichloroethyl sulphide. 

With Ammonia. Dichloroethyl sulphide reacts only mildly 
with gaseous ammonia even on heating to 150° C. However, 

1 J. Davies and Oxford, /. Chem. Soc, 1931, 234. 

2 J. Davies and Oxford, /. Chem. Soc, 1931, 235. 



DICHLOROETHYL SULPHIDE 239 



with alcoholic ammonia on heating to 60° C. under pressure, the 
reaction is vigorous 1 and 1-4 thiazane is formed as follows : 

/CHj-CHoCl /CH 2 -CH A 
S( + NH 3 = S( /NH + 2 HC1 

CH 2 — CH 2 C1 CH 2 — CH 2 

This is a colourless liquid with an odour of pyridine, boiling at 
169° C. at 758 mm. of mercury. It fumes in the air and is miscible 
with water and with the common organic solvents. On exposure 
to the air it absorbs carbon dioxide. 

With Aliphatic Amines, In presence of sodium carbonate, 
dichloroethyl sulphide reacts with the aliphatic amines in alcoholic 
solution as follows 2 : 

+ RNH 2 S( )NR + 2 HC1 

CH 2 CH 2 C1 CH 2 CH 2 

Several compounds of this type have been prepared. They are 
in general colourless mobile oils with densities less than unity. 
The following are the principal : 

4 Methyl 1-4 thiazane, b.p. 163° to 164° C. at 757 mm. Density 
6*9959 at 15 0 C. Completely miscible with water and with various 
organic solvents. 

4 Ethyl 1-4 thiazane, b.p. 184 0 C. at 763 mm. Density 0-9929 
at 15 0 C. Soluble in water. 

4 Phenyl 1-4 thiazane, m.p. 108° to 111° C. A white powder, 
soluble in hot toluene. 

With Potassium Cyanide, By the action of potassium cyanide 
on dichloroethyl sulphide dissolved in alcohol, dicyanoethyl 
sulphide is not formed, but a crystalline substance separates 
(m.p. 91 0 C.) of the formula C 6 H 12 S 2 (CN) 2 which, later researches 3 
have shown, has the structure 

CN— CH 2 — CH 2 — S— CH 2 — CH 2 — S— CH 2 — CH 2 — CN. 

Dicyanoethyl sulphide has been obtained, however, by boiling 
sodium sulphide with the nitrile of /S chloropropionic acid, 
dissolved in alcohol : 

/CH 2 CH 2 CN 

2 CH 2 C1-CH 2 CN + Na^ = 2 NaCl + 

1 W. Davies, /. Chem. Soc, 1920, 117, 299; Clarke, /. Chem. Soc, 1912, 
101, 1585. 

2 Lawson and Reid, /. Am. Chem. Soc, 1925, 47, 2821 ; Clarke, loc cit. 
» Clarke, loc. cit. ; Davies, loc. cit. 



240 



SULPHUR COMPOUNDS 



It forms crystals, melting at 24° to 25° C, which have no 
vesicatory properties. 1 

With Sodium Selenide. By boiling dichloroethyl sulphide with 
an aqueous solution of sodium selenide, 1-4 selenothiane is 
formed 2 : 

/CH 2 CHa 
S( /Se 
CH 2 CH 2 



This is obtained in thin colourless leaflets, melting at 107° C. It 
boils at a pressure of 97 mm. of mercury at 86-5° C, and behaves 
chemically in a similar manner to dithiane. 

With Methyl Iodide. Dichloroethyl sulphide reacts with methyl 
or benzyl iodide, forming the corresponding sulphonium salt. 
For instance, with methyl iodide, dithiane methiodide is formed : 

/CH 2 CH 2 \ /CH 3 
CH S CH 2 I 

This is a crystalline substance melting at 174° C, easily soluble 
in hot water, soluble with difficulty in alcohol and insoluble in 
ether. 3 

With Magnesium Phenylarsine. By treating dichloroethyl 
sulphide in hot benzene solution with magnesium phenylarsine in 
ethereal solution, phenyl thioarsane is formed 4 : 

/CH 2 CH 2 C1 /CH 8 CH 2 \ 
S< f C 6 H 5 AsMg = S( >AsC 6 H 5 + MgCl 2 

N CH 2 CH 2 C1 X CH 2 CH/ 



as crystals with m.p. 38° C. It boils at 134° C. at a pressure of 
4 mm. of mercury. It forms additive compounds with mercuric 
chloride. 

Like the other cyclic sulphides, it has no vesicant action and 
only a weak toxicity. 

With Zinc and Ethyl Alcohol. When an alcoholic solution of 
dichloroethyl sulphide is treated on the water-bath with zinc 
dust, a very complex reaction takes place and various compounds 
are formed : ethylene, hydrogen sulphide, hydrochloric acid, 

1 Nekrassov, /. Rusk. Fis. Khim. Obsc, 1927, 59, 921. 

2 C. S. Gibson and J. Johnson, /. Chem. Soc, 1933, 1529. 

3 C. Nenitzescu and Scarlatescu, Ber., 1934, 67> 1142. 
* Jobb and coll., Bull. soc. chim., 1924, 35, 1404. 



DICHLOROETHYL SULPHIDE 



dithiane, ethyl sulphide, vinyl ethyl sulphide, ethyl mercaptan, 
etc. The principal product is diethyl thioglycol 1 : 

/CHaCH^OCaH,, 

\:h 2 ch s oc 2 h 5 

This is a liquid boiling at 225° C. at a pressure of 746 mm. 
Density 0-9672 at 20° C. It is volatile in steam, sparingly soluble 
in water, but soluble in the organic solvents. It has no vesicant 
power. 

Various other condension products of dichloroethyl sulphide 
have been prepared, such as those with phenates, thiophenates, 
mercaptides and aromatic amines, and in every case the physical, 
chemical and biological properties of these have been studied. 2 

With Metallic Salts. Like various other organic sulphides, 
dichloroethyl sulphide readily reacts with the salts of the heavy 
metals. Thus with gold or platinum chloride, compounds are 
formed which, being insoluble in water, may be employed for the 
detection of the sulphide (see p. 248). With copper or mercury 
chloride stable additive chlorides are formed of the following 
type: 

[(C1CH 2 — CH 2 ) 2 S] 2 .Cu 2 Cl 2 . 

These may be employed to determine dichloroethyl sulphide 
quantitatively (see p. 251). Tin and titanium chlorides similarly 
form additive products. 3 

Ferric chloride decomposes dichloroethyl sulphide, forming 
various halogenated vinyl compounds. 4 

With Metals, At ordinary temperatures the action of pure 
dichloroethyl sulphide on steel, iron, lead, aluminium, zinc and 
tin is practically nil. At higher temperatures, about 100° C, 
steel is slightly corroded, but aluminium and lead are not 
attacked (Gibson and Pope). 

On warming in contact with iron, especially in presence of 
water, dichloroethyl sulphide is decomposed to form thiodiglycol, 
hydrogen sulphide, diethylene sulphide and its polymers, 
hydrochloric acid, hydrogen, ethylene and ethylene dichloride. 

The action of crude dichloroethyl sulphide on the steel walls of 
projectiles has been studied by W. Felsing and H. Odeen. 5 They 
have observed that in projectiles charged with dichloroethyl 

1 Kretov, /. Rush. Fis. Khim. Obsc, 1929, 61, 2345. 

2 Helfrich and Reid, /. Am. Chem. Soc, 1920, 42, 1208, 1232 ; Fromm and 
Jorg, Ber., 1925, 58, 305. 

3 Jackson, Chem. Reviews, 1934, 443- 

4 Grignard, Ann. chim., 1921, [9] 15, 5. 

* W. Felsing and H. Odeen, /. Ind. Eng. Chem., 1920, 12, 1063. 



242 



SULPHUR COMPOUNDS 



sulphide (prepared by Levinstein's method, see p. 223) the 
internal pressure increased on maintaining at 60° C. for 8 days 
to about 2 atmospheres. The degree of decomposition of' the 
sulphide was negligible, and the increase in acidity amounted to 
about 1%. 

The outstanding physiopathological property of dichloroethyl 
sulphide is its vesicant action. The first symptoms of this action 
appear after 4-6 hours, but sometimes the latent period may 
extend to 24 hours. 

The sensitivity of the skin to dichloroethyl sulphide varies 
with the individual. Fair people are more sensitive than dark 
and the latter more sensitive than negroes. 1 

Exposure even for a short time (a few minutes) to a concentra- 
tion of 0-2 mgm. of the vapours of dichloroethyl sulphide per cu. m. 
of air causes irritation, according to Gilchrist, 2 without, however, 
visible lesions. 

On contact of liquid dichloroethyl sulphide with the skin, 
erythema is produced with 0-12 mgm. per sq. cm. of skin and 
blisters with 0*5 mgm. per sq. cm. of skin. 

On inhalation, according to American experiments, 3 fatal 
results follow exposure of 10 minutes to a concentration of 
150 mgm. per cu. m. of air, or exposure of 30 minutes to a 
concentration of 70 mgm. per cu. m. of air. 

Mortality-product : 1,500 according to both Miiller and Prentiss. 

For the decontamination of the skin, washing with hot soapy 
water is very efficacious. 4 

For the decontamination of objects, Renwanz 5 recommends 
the use of bleaching powder (see p. 231). 

For the decontamination of glass materials, concentrated nitric 
acid may v be employed. 6 This must be carried out with care 
because in the somewhat violent reaction liquid may be thrown 
out by the violent evolution of nitrous gases. 

The decontamination of paper, print, documents, etc., may be 
carried out by exposing such objects to the action of gaseous 
ammonia in closed containers for several days. 7 

1 G. Ferri, " Ricerche sulla sensibility individuate della cute umana all'iprite 
e sopra alcuni fattori capaci di modificarla " (" Researches on individual 
sensitivity of the human skin to mustard gas and on some factors which can 
modify this "), Giornale di Medicina Militare, September, 1937. 

* Gilchrist, The Residual Effects of Warfare Gases, II, U.S. Government 
Printing Office, Washington, 1933. 

a Prentiss, op. cit. 

4 S. Przychocki, Heeressanitdtswesen, 1934, 23, 5, 6, Warsaw ; Gasschutz und 
Luftschutz, 1936, 28. 

* G. Renwanz, Die Gasmaske, 1935, 1. 

6 Weidner, Gasschutz und Luftschutz, 1936, 133. 

7 Zernik, Archiv. Zeitschr., 1936, 44, 185. 



DIBROMOETHYL SULPHIDE 



243 



2. Dibromoethyl Sulphide (M.Wt. 247 8) 

s/ CH 2 — CH 2 Br 



3 \ 

C H 2 — CH2Br 

)8)8' dibromoethyl sulphide was examined as a possible war gas 
only in the post-war period (Muller). Although having similar 
physiopathological properties to dichloroethyl sulphide, it has 
some disadvantages as a war gas, especially from the manufactur- 
ing point of view (Hanslian). 

Steinkopf 1 prepared dibromoethyl sulphide by the action of 
phosphorus tribromide on thiodiglycol. However, it may be 
prepared more simply by saturating an aqueous solution of 
thiodiglycol with hydrobromic acid. 2 

It may also be prepared, according to Kretov, 3 by the action 
of hydrobromic acid or phosphorus tribromide on diethoxyethyl 
sulphide (see p. 238). 

/CH 1 CH J OC 1 H, /CH 2 CH 2 Br 
S\ +-4 HBr = S( +2 C 2 H 5 Br + 2 H,0 

X CH 2 CH 2 OC 2 H 5 * X CH 2 CH 2 Br 2 

Laboratory Preparation 2 

976 gm. thiodiglycol are dissolved in 400 ml. water in a flask 
fitted with a reflux condenser and a gas inlet-tube. It is cooled 
in ice and saturated with hydrobromic acid. The mixture is then 
heated to about 80° C. and more hydrobromic acid bubbled in 
until the reaction is complete. On cooling, the dibromoethyl 
sulphide solidifies, separating at the bottom of the flask. The 
aqueous layer is decanted off and the solid product washed with 
cold water and crystallised from ether. Yield 95%. 

Physical and Chemical Properties 

Dibromoethyl sulphide forms white crystals which melt at 
31° to 34° C. (Steinkopf). It boils at ordinary pressure at 240° C. 
with decomposition and at 1 mm. pressure at 115*5° C. 

The specific gravity at 15° C. is 2-05. It is insoluble in water 
and soluble in alcohol, ether and benzene. 

The volatility at 20° C. is about 400 mgm. per cu. m. It is 
more rapidly decomposed by water than dichloroethyl sulphide. 4 

1 Steinkopf, Ber., 1920, 53, 1011. 

2 Burrows and Reid, /. Am. Chem. Soc, 1934. 56, 1720, 1722. 

3 Kretov, /. RusK. Fis. Khim. Obsc, 1929, 61, 2345. 

4 Rona, Z. ges. expt. Med., 1921, 13, 16 ; Muller, Die Chemische Waffe, 
Berlin, 1932, 84, 111. 



244 



SULPHUR COMPOUNDS 



On treating a hot solution of dibromoethyl sulphide in chloro- 
form with benzoyl hydrogen peroxide, dibromoethyl sulphoxide 
is formed : 

/CH 2 CH 2 Br 

os( 

CH 2 CH 2 Br 

This forms glittering crystals melting at 100° to 101° C. 1 It may 
also be* obtained by the action of concentrated nitric acid on 
dibromoethyl sulphide by first maintaining the temperature at 
o° C. and then allowing it to rise to room temperature to complete 
the reaction. 2 

Chromic anhydride and dilute sulphuric acid react at water- 
bath temperature with dibromoethyl sulphide to produce 
dibromoethyl sulphone 2 : 

/CH,CH 2 Br 

o 2 s( 

CH 2 CH 2 Br 

which forms plates melting at 111° to 112° C. 

Dibromoethyl sulphide, like the dichloro-compound, easily 
reacts with primary amines', forming the corresponding thiazane 
derivatives (Burrows). 

It reacts with methyl iodide more readily than dichloroethyl 
sulphide, forming dithiane methiodide 3 : 

/CH 2 CH 2 \ /CH 3 

S \ / S \ 
CH 2 CH 2 I 

The persistence of dibromoethyl sulphide on the ground is 
greater than that of dichloroethyl sulphide only in dry weather. 

The physiopathological properties are similar to those of 
dichloroethyl sulphide according to Meyer, 4 but milder. 

3. Diiodoethyl Sulphide (M.Wt. 341-8) 

/CH 2 — CH 2 I 

S \ 

CH 2 — CH 2 I. 

/?/?' diiodoethyl sulphide was not used as a war gas during the 
war of 1914-18, in spite of its great toxic power. It was obtained 

1 Lewin, /. prakt. Chem., 1930, 127, 77. 

2 Burrows and Reid, /. Am. Chem. Soc, 1934, 56, 1720. 

3 Nenitzescu and Scarlatescu, Ber., 1934, 67, 1142. 
* A. Mayer, Compt. rend., 1920, 170, 1073. 



DIIODOETHYL SULPHIDE 



245 



by Helfrich 1 in 1920 by treating dichloroethyl sulphide with 
sodium iodide in alcoholic solution. 

It is produced in the reaction between dichloroethyl sulphide 
and the Grignard reagent (see p. 248), and also, together with 
dithiane methiodide, by the action of methyl iodide on dichloro- 
ethyl or dibromoethyl sulphide. 2 It has also been obtained by 
the action of hydriodic acid on an aqueous solution of divinyl 
sulphide. 3 

Preparation 

Diiodoethyl sulphide is prepared according to Grignard by 
treating dichloroethyl sulphide with sodium iodide in acetic acid 
solution and heating to 60° C. On pouring the product into 
water, a crystalline product is obtained and this is then purified 
by recrystallisation. 

Physical and Chemical Properties 

Diiodoethyl sulphide forms bright yellow prisms melting at 
62° C. according to Grignard, 4 and at 68° to 70° C. according to 
Kretov. 6 

It decomposes in time, especially if exposed to light, or on 
heating even to 100° C. 

It is insoluble in water and soluble in the common organic 
solvents. On treatment with alkali it is readily hydrolysed. 
With oxidising agents it is converted into diiodoethyl sulphoxide 
(white crystals, melting at 104-5° C.) or into diiodoethyl sulphone 
(small white needles, m.p. 203° C.) This latter compound has 
also been prepared by the action of hydriodic acid on thioxane 
sulphone 8 : 



Diiodoethyl sulphide reacts with methyl iodide more readily 
than the dichloro- compound to form dithiane methiodide 7 : 



1 Helfrich and Reid, /. Am. Chem. Soc, 1920, 42, 1208, 1232. 

2 Nenitzescu and Scarlatescu, Ber., 1934, 67, "4 2 - 

8 J. Alexander and McCombie, /. Chem. Soc, 1931, 1913. 

* Grignard and Rivat, Ann. chim., 1921, 15, 5. 

6 Kretov, /. Rusk. Fis. Khim. Obsc, 1929. 61, 2345. 

6 Fromm and Ungar, Ber., 1923, 56, 2287. 

7 J. Alexander and McCombie, loc. cit. 




CH 2 CH 2 I 
CH0CH0I 



+ H a O 




246 



SULPHUR COMPOUNDS 



Diiodoethyl sulphide has a vesicant action on the skin similar 
to that of dichloroethyl sulphide (Helfrich). 

Analysis of the Sulphides 

Detection of Dichloroethyl Sulphide 

The following reagents have been proposed for the detection of 
dichloroethyl sulphide 1 : 

Potassium Permanganate. A 0-003% solution of potassium 
permanganate, acidified with a few drops of sulphuric acid, is 
decolourised by air containing dichloroethyl sulphide vapour. 
The minimum quantity of the sulphide producing a distinct 
colour-change is about 0-15 mgm., according to Spica. 2 

/? Naphthol. On passing dichloroethyl sulphide vapours 
through an alcoholic and strongly alkaline solution of /? naphthol, 
a turbidity is produced which slowly settles. The j8 naphthol 
solution is prepared by adding 100 ml. N/50 sodium hydroxide 
solution to 1 ml. of a 10% alcoholic solution of /? naphthol. As 
this mixture turns brown on keeping, the two solutions should 
not be mixed until just before using. 

In order to detect very low concentrations of dichloroethyl 
sulphide it is necessary to pass the gas for 10-15 minutes. With 
this reagent as little as 0-06 mgm. dichloroethyl sulphide may be 
recognised. 

Congo Red Paper. Detection by means of this paper depends 
on the formation of hydrochloric acid by the decomposition of 
dichloroethyl sulphide with sulphuric acid. The gas to be 
examined is passed through a wash-bottle containing concentrated 
sulphuric acid at 55° C, and then over the Congo red test-paper. 

Sodium Iodoplatinate Paper. This test-paper changes from its 
original pink colour to violet by the action of dichloroethyl 
sulphide, the intensity of the violet varying with the concentration 
of dichloroethyl sulphide. The papers are prepared by immersing 
strips of filter paper in an aqueous 0-2% solution of sodium 
iodoplatinate just before use. To test for the presence of 
dichloroethyl sulphide, the treated paper is exposed in a damp 
condition to the gas to be examined. Sensitivity 0-02 mgm. 
(Spica) . 

Potassium Mercuri-iodide. On passing air containing dichloro- 
ethyl sulphide vapour through an aqueous solution of potassium 
mercuri-iodide a whitish-yellow precipitate separates. If the 

1 Schroter, Z. angew. Chem., 1936, 164, gives a risumi of the methods 
proposed for the detection of dichloroethyl sulphide. 
* Spica, Gazz. chim. ital., 1919, 49, 299. 



DICHLOROETHYL SULPHIDE: DETECTION 247 



quantity of dichloroethyl sulphide is very small the reaction may 
be aided by warming to 40 0 to 50 0 C. The limit of sensitivity is 
0-03 mgm. 

The reagent is prepared by dissolving 10 gm. potassium iodide 
in 70 ml. water and adding 14 gm. mercuric iodide. 

This reaction is given by the alkaloids, as well as by 
dichloroethyl sulphide. 

A method for the quantitative determination of dichloroethyl 
sulphide has also been based on this reaction. 1 

Hydrogen Peroxide. When air containing dichloroethyl sulphide 
is passed through a solution containing 30% by volume of 
hydrogen peroxide in acetic acid, colourless acicular crystals are 
formed, first in the air-inlet tube and then in the liquid. 

Sodium Monosulphide. On passing air containing dichloroethyl 
sulphide through a concentrated solution of sodium monosulphide, 
a white turbidity is produced, due to the formation of diethylene 
disulphide of the following structure (see p. 236) : 



In carrying out this test in practice, Spica 2 recommends that 
the air under examination be passed through a U-tube of 4-5 mm. 
diameter, having a small bulb at the bend in which a few drops of 
the reagent are placed. In passing over the reagent, the air 
produces the characteristic turbidity. 

Data of the sensitivity of the last two reagents are not known. 
None of the reagents described above is adapted for the detection 
of dichloroethyl sulphide in its war-gas application, either because 
of low sensitivity or because of similar reactions with other 
substances. 

During the war of 1914-18 the following reagents were 
employed : 

Yablich's Reagent. 3 This reagent was suggested by the Chemical 
Warfare Service and was especially employed by the Americans. 
It is based on the fact that when air containing dichloroethyl 
sulphide is passed through a solution of selenious acid in dilute 
sulphuric acid and then the reagent is heated for about 10 minutes 
at 85° C, a yellow precipitate of metallic selenium is produced 
(see p. 233). If the amount of dichloroethyl sulphide present is 
small, a reddish-orange suspension appears. The reagent is 




1 L. Buruiana, Z. anal. Chem., 1937, 109, 107. 

3 Spica, Gazz. chim. Hal., 1919, 49, 299. 

3 M. Yablich, /. Am. Chem. Soc, 1920, 42, 266. 



248 



SULPHUR COMPOUNDS 



prepared by dissolving 1 gm. Se0 2 in 100 ml. of a solution 
containing equal parts by weight of sulphuric acid and water. 
Although many war gases give a negative reaction with this 
reagent, all the arsine derivatives give as positive a result as does 
dichloroethyl sulphide. A similar reaction is also given by carbon 
monoxide and hydrogen sulphide. 
Sensitivity : 5 mgm. dichloroethyl sulphide per cu. m. of air. 1 
Grignard's Reagent. 2 This reagent, which is fairly specific for 
dichloroethyl sulphide, was proposed by Grignard in 1918, but 
was kept secret until 1921. Detection is based on a double 
decomposition reaction of a type fairly frequent in organic 
chemistry : 

S(C 2 H 4 C1) 2 + 2HI = S(C 2 H 4 I) 2 + 2HCI. 

The dichloroethyl sulphide is converted to diiodoethyl sulphide 
which separates as yellow crystals. 

Grignard's contribution was to define the conditions which 
made the test highly sensitive and capable of being carried out 
rapidly without employing heat. 

Preparation of the reagent : 

Sodium iodide 20 gm. 

7 "5% copper sulphate solution. . . 40 drops 
35% gum arabic solution . . . 2 ml. 

Water 200 ml. 

The copper sulphate is added in order to catalyse the reaction, 
while the gum arabic causes the diiodoethyl sulphide to separate 
in the colloidal form instead of crystalline. 

For the detection of dichloroethyl sulphide, the air under 
examination is passed through the reagent prepared as described 
above. In the presence of dichloroethyl sulphide a yellow 
precipitate of diiodoethyl sulphide separates. According to 
Grignard, 100 mgm. dichloroethyl sulphide may be detected in 
1 cu. m. of air in 4 minutes. 

It has been found that while the aliphatic arsines and phenyl 
carbylamine chloride produce a similar turbidity at high con- 
centration (4%), other substances such as mono-, di- and tri- 
chloromethyl chloroformates, chloropicrin, benzyl bromide, 
acrolein, the aromatic arsines, thiodiglycol, etc., do not react. 

Recently the following method has been elaborated : 

SchrGter's Method. This is based on the property of dichloro- 
ethyl sulphide of forming additive-compounds with gold and 
palladium chlorides (see p. 241). 

1 Flury and Zernik, Schddliche Gase, Berlin, 1931, 367. 

» V. Grignard, Rivat, and Schatchard, Ann. chim., 1921, 15, 5. 



DICHLOROETHYL SULPHIDE : DETERMINATION 249 



On treating an aqueous solution containing o-i% gold chloride 
or 0-05% palladium chloride with dichloroethyl sulphide a 
turbidity of colloidal type quickly forms, and if the quantity 
of the sulphide is large, yellowish-red oily droplets are 
produced. 

This reaction may also be carried out on filter paper. In this 
case a reddish-brown stain is formed with a 10% gold chloride 
solution and a yellow stain with a 0-2% palladium chloride 
solution. 

According to Obermiller, 1 these reactions are specific for 
dichloroethyl sulphide and are not influenced by the presence of 
any other war gas, nor by the hydrolysis products of dichloroethyl 
sulphide. 

The sensitivity with gold chloride is of the order of 10 mgm. 
dichloroethyl sulphide per cu. m. of air. 

An apparatus has been designed for detecting the presence of 
dichloroethyl sulphide in a sample of air by this reaction. 2 The 
air is drawn by means of a small pump through a glass tube 
containing silica-gel, to which are added, after a certain number 
of strokes of the pump, several drops of gold chloride solution. 
A little more air is drawn through the tube and then a few drops 
of hydrogen peroxide are added. 

In the presence of dichloroethyl sulphide a yellow ring forms. 

Sensitivity : 12 mgm. of the sulphide per cu. m. of air. 3 

Quantitative Determination of Dichloroethyl Sulphide 
in Air 

Nephelometric Method of Yablich. 4 ' This method depends on 
the reduction to metallic selenium, in the form of an orange-yellow 
suspension, of selenious acid when it reacts with dichloroethyl 
sulphide, and on the nephelometric measurement of the suspension 
formed. 

The selenious acid employed in this method of analysis is 
prepared by dissolving 1 gm. Se0 2 in 100 ml. of an aqueous 
solution of sulphuric acid (1 : 1 by weight). 

In practice the determination is carried out by bubbling the 
mixture of air and dichloroethyl sulphide through the reagent 
and then heating to 85 0 C. for 10 minutes. The solution is then 
allowed to cool and the quantity of gas present obtained by 
nephelometric comparison with a standard solution. 

1 Obermiller, Z. angew. Chem., 1936. 49, 162. 

2 Schroter, Z. angew. Chem., 1936, 49, 164. 

3 Stampe, Drager-Hefte, 1935, No. 180, 2966. 

4 Yablich and coll., /. Am. Chem. Soc, 1920, 42, 266, 274. 



250 



SULPHUR COMPOUNDS 



By this method quantities of dichloroethyl sulphide may be 
determined of the order of o-i-o-ooi mgm. with a maximum 
error of 0-005 mgm. 

The Potentiometric Method of Hopkins. Another method of 
determining small quantities of dichloroethyl sulphide in air has 
been proposed by Hopkins. 1 It consists in hydrolysing the 
dichloroethyl sulphide with water at 35° C. and determining the 
hydrogen ion concentration of the solution obtained by a 
potentiometric method. 

In carrying out this determination it is recommended that the 
gas should be bubbled through two tubes in series containing 
water at 35 0 C. In this way the dichloroethyl sulphide is 
hydrolysed rapidly and by measuring the hydrogen ion concentra- 
tion of the solution (methyl red indicator) the quantity of 
dichloroethyl sulphide may be obtained. 

Maxim's Method. This is based on the oxidation of the 
sulphur atom in dichloroethyl sulphide and its determination as 
barium sulphate. 2 

It is carried out by passing the gas containing dichloroethyl 
sulphide first through an ordinary combustion tube (whose length 
is chosen according to the quantity of gas to be examined), filled 
with fragments of pumice and heated to redness, and then through 
a wash-bottle containing a 20% solution of barium chloride and 
10-20 ml. hydrogen peroxide. The dichloroethyl sulphide on 
passing through the combustion tube is converted into sulphur 
dioxide and this is oxidised to sulphuric acid and precipitated as 
barium sulphate. 

Quantitative Determination of Dichloroethyl Sulphide 
in Industrial Products 

The method commonly used up to the present to determine 
the dichloroethyl sulphide content of industrial products 
consists in distilling a certain quantity of the sample to be 
examined at reduced pressure (40 mm.) and collecting the 
fraction boiling between 125 0 and 130 0 C. From the volume 
of this fraction the purity of the product may be estimated 
approximately. 

Two other methods which have been proposed are described 
below. 

Hollely's Method. 3 This method is based on the reaction 
1 Hopkins, /. Pharmacol., 1919, 12, 393, 403. 

a M. Maxim, Chem. Zeit., 1932, 56, 503 ; Redlinger, Chem. Zeit., 1932, 56, 
704. 

3 W. Hollely, /. Chem. Soc, 1920, 117, 898. 



DICHLOROETHYL SULPHIDE : DETERMINATION 251 



between dichloroethyl sulphide and cuprous chloride, forming a 
double salt of definite composition : 

rClCH 2 -CH 2 \ -1 



Description of the Method : About 1 gm. of the sample is 
weighed accurately into a 100 ml. flask with a tight stopper. 
10 ml. of a solution of cuprous chloride in absolute alcohol 
containing hydrochloric acid 1 are added and the mixture 
continually agitated, without heating, for 10 minutes so as to 
ensure complete solution of the dichloroethyl sulphide. At the 
end of this time, the mixture is cooled with water and still 
agitated while 50 ml. of a 5% aqueous solution of sodium chloride 
are added from a burette. A precipitate of the double salt 
separates as fine colourless needles. After allowing to stand for 
a short time, the solution is filtered through glass wool, the 
filtrate being collected in a dry receiver. The excess cuprous 
chloride in the filtered liquid is then estimated in the following 
manner : 

30 ml. of the nitrate are measured into a 250 ml. flask by means 
of a burette and 5 ml. 20 volume hydrogen peroxide are added 
to oxidise the copper to the divalent condition. 

The contents of the flask are then boiled, being taken almost 
to dryness and taken up with water several times (generally 
twice) so as to remove the hydrogen peroxide completely. The 
residue is diluted once more with 50 ml. water and a solution of 
sodium carbonate added until a slight precipitate is formed, 
this being then redissolved with a few drops of dilute acetic acid. 
Excess potassium iodide is added and the liberated iodine is 
titrated with a decinormal solution of sodium thiosulphate. 

At the same time the alcoholic cuprous chloride solution is also 
titrated with the same thiosulphate solution, after first oxidising 
the cuprous chloride with 5-10 ml. hydrogen peroxide and 
following the procedure described. 

From the results of this determination, the percentage of 
dichloroethyl sulphide present in the original sample may be 
obtained by the following calculation : 

From the formula of the double salt, it follows that 127 gm. 
copper correspond to 318 gm. dichloroethyl sulphide, and as 
1 ml. N/10 thiosulphate is equivalent to 0-00635 gm. copper, 

1 The solution of cuprous chloride must be prepared freshly immediately 
before use , and it is therefore advisable to have a i o % solution of hydrochloric acid 
in absolute alcohol available, and to dissolve 5 gm. of cuprous chloride in 50 ml. 
of this immediately before use. 




252 



SULPHUR COMPOUNDS 



i ml. thiosulphate must correspond to 0-0159 S 1 * 1 - dichloroethyl 
sulphide. 

Therefore the percentage will be given by the formula : 

(A — B) X 0-0159 X 100 
% dichloroethyl sulphide = weig ht of sample 

in which 

A = ml. N/10 thiosulphate equivalent to the copper in 10 ml. 
of the solution tested as a blank. 

B = ml. N/10 thiosulphate equivalent to the excess copper in 
10 ml. of the solution after reaction with dichloroethyl sulphide. 

The volume resulting from the admixture of 10 ml. cuprous 
chloride solution with 50 ml. 5% sodium chloride solution has 
been experimentally found to be 59-5 ml. instead of 60 ml. 

This method of determining dichloroethyl sulphide does not 
give exact results when thiodiglycol and chlorinated derivatives 
of dichloroethyl sulphide are present in the sample (Jackson). 

The Method of Grignard, Rivat and Schatchard. 1 This method is 
based on the conversion of dichloroethyl sulphide to diiodoethyl 
sulphide by means of hydriodic acid in acetic acid solution : 

✓CH 2 — CH 2 C1 /CH 2 — CH 2 I 
S< +2HI = S< " +2HCI. 

X CH 2 — CH 2 C1 X CH 2 — CH 2 I 

and on the determination of the quantity of hydriodic acid which 
has not reacted. 

Description of the Method : (1) The total iodine present in the 
hydriodic acid to be employed is first determined. 15 ml. glacial 
acetic acid are placed in a flask, and 5 ml. of a solution containing 
about 54% hydriodic acid added from a burette. A tube to 
serve as air condenser is fitted to the flask ; its upper end should 
be drawn out and bent over to prevent dust entering. The mixed 
acids are then warmed on the water-bath for 15 minutes to 70° C. 
After cooling and diluting to 50 ml. , 10 ml. of 10% sodium nitrite 
solution are added to liberate the iodine. 

The iodine is extracted with carbon tetrachloride (once with 
20 ml. and four times with 10 ml.) and all the extracts are added 
to 100 ml. distilled water. The mixture is shaken to wash the 
tetrachloride, the water separated and shaken with a little carbon 
tetrachloride which is then added to the main bulk of the 
tetrachloride. The solution of iodine is finally titrated with 
thiosulphate and starch solution. 

Let A 0 be the number of ml. of thiosulphate used. 

(2) The procedure described under (1) is followed, about 1 gm. 

1 Grignard and coll., Ann. chim., 1921, 15, 5, 18. 



SULPHURIC ACID DERIVATIVES 



of dichloroethyl sulphide (weighed accurately = P gm.) being 
added to the acetic acid solution. After heating and subsequently 
cooling, the contents of the flask (crystals and liquid) are poured 
into a tared 500 ml. graduated flask containing 100 ml. carbon 
tetrachloride and 200 ml. water. 

The flask is shaken to dissolve the diiodoethyl sulphide, the 
contents diluted to volume and shaken again to homogenise the 
solution. After allowing to stand so that the two liquids separate, 
50 ml. of the aqueous layer are taken, the iodine liberated with 
sodium nitrite and titrated as in (1). 

Let A x be the number of ml. of thiosulphate used. 

The 100 ml. of carbon tetrachloride are decanted from the 
flask, the latter washed with a little carbon tetrachloride which 
is then added to the main bulk of tetrachloride and the free 
iodine in the whole titrated. 

Let A 2 be the number of ml. of thiosulphate used. 

Then the percentage of dichloroethyl sulphide is given by the 
formula : 

% dichloroethyl sulphide = ^Jr [ io ^ 0 + 1-5 — (&4 X + A 2 )~\ 

There are no indications in the literature of the repeatability 
or accuracy of the results obtained by this method. 



(C) CHLOROANHYDRIDES AND ESTERS OF SULPHURIC ACID 

Being dibasic, sulphuric acid can form two chloroanhydrides, 
chlorosulphonic acid and sulphuryl chloride. 




While chlorosulphonic acid may be considered as the acid 
chloroanhydride of sulphuric acid, sulphuryl chloride is the true 
chloroanhydride. The chlorine atom in these compounds, as in 
all the chloroanhydrides, has little stability ; it is readily split 
off by water. However, while chlorosulphonic acid reacts with 
water with great readiness, sulphuryl chloride reacts very 
slowly. 

Chlorosulphonic acid has little toxicity and has been chiefly 
employed in warfare as a smoke producer. Sulphuryl chloride 
was used particularly in admixture with other war gases (cyanogen 
chloride, chloropicrin, etc.). 



254 



SULPHUR COMPOUNDS 



Sulphuric acid forms two types of esters like the two types of 
chloroanhydrides : 




monoalkyl ester dialkyl ester 



Of these esters, methyl sulphuric acid and dimethyl sulphate 
were employed as war gases. They have great toxic power and 
act on the respiratory passages and on the skin. 

These esters are insoluble in water though they are decomposed 
on contact with water to split off the alkyl group, especially 
dimethyl sulphate. This same scission also takes place in presence 
of other substances containing the hydroxyl group. It is for this 
reason that dimethyl sulphate is widely employed both in the 
laboratory and in industry as a methylating agent. 

Furthermore, beside the chloroanhydrides and the esters 
already mentioned, sulphuric acid can form compounds of mixed 
type, of the general formula : 




These compounds, which may be considered as chloroanhydrides 
of alkylsulphuric acids, have little stability. They are readily 
decomposed by cold water or by the action of the alkali hydroxides 
with splitting off of the halogen and formation of the alkyl 
sulphuric acids : 

/OR /OR 
S0 2 < + H a O = S0 2 ( + HCl 
N C1 N OH 

It is interesting to consider the behaviour of these substances 
to the hydrolysing action of water, mentioned above. While the 
ethers readily split off the alkyl group, the chloroanhydrides of 
the alkyl sulphuric acids contain an alkyl which is not easily 
removed. It seems that in the latter compound the chlorine 
atom hinders the hydrolytic process. 

In the war of 1914-18 methyl chlorosulphonate and ethyl 
chlorosulphonate were employed as war gases. Owing to the 
presence of halogen in their molecules, these substances have a 
powerful lachrymatory action, but their toxicity is less than that 
of the sulphates. 



CHLOROSULPHONIC ACID 



255 



Since the war several other homologues of methyl chloro- 
sulphonate have been prepared and studied, 1 for instance : 
Propyl Chlorosulphonate 

so/ 

N C1 

which is obtained by the action of sulphuryl chloride on w-propyl 
alcohol. It boils at 70° to 72 0 C. at a pressure of 20 mm. 

Also halogenated derivatives of ethyl chlorosulphonate : 

Chloroethyl Chlorosulphonate 

/OCH 2 • CH 2 C1 
S0 2 ( 

obtained by the action of sulphuryl chloride on glycol 
chlorohydrin, boils at 101 0 C. at 23 mm. pressure and has an 
odour similar to that of chloropicrin. 
Bromoethyl Chlorosulphonate 

,OCH,CH,Br 
X C1 

obtained by the action of sulphuryl chloride on glycol bromo- 
hydrin, boils at ioo° to 105 0 C. at 18 mm. pressure. 

These three compounds are powerful lachrymators. 

Several analogous compounds have also been prepared, such 
as methyl fluorosulphonate and ethyl fluorosulphonate. These are 
liquids with ethereal odours, having both lachrymatory and toxic 
properties. The ethyl derivative has greater lachrymatory power 
than the methyl. 2 

Further, a chlorinated derivative of dimethyl sulphate has 
been prepared, dichloromethyl sulphate (see p. 257). This is a 
colourless liquid boiling at 96° to 97° C. at 14 mm. of mercury. 
Unlike dimethyl sulphate, this compound is completely destitute 
of toxic power. 8 

1. Chlorosulphonic Acid (M.Wt. 116-53) 

.CI 

so/ 

x OH 

Chlorosulphonic acid was used as a war gas in small quantities 
in the war of 1914-18 by the French and also by the Germans, but 

1 W. Steinkopf and coll., Ber., 1920, 53, 1144 ; R. Levaillant, Compt, rend., 
1928, 187, 730. 

2 J. Meyer and G. Schramm, Z. anorg. Chem., 1932, 206, 27. 

3 Fuchs and Katscher, Ber., 1927, 60, 2293. 



256 



SULPHUR COMPOUNDS 



its principal use was as a smoke producer. The French employed 
it with dimethyl sulphate in the mixture " Rationite." 

Preparation 

Chlorosulphonic acid is formed by the simple addition of 
hydrochloric acid to sulphur trioxide : 



The usual method of preparation of chloroanhydrides may also 
be employed : 



In the laboratory, chlorosulphonic acid is usually prepared by 
the method of Beckurts and Otto. 1 

200 gm. oleum (containing 38-40% free S0 3 ) is placed in a 
tubulured retort of about 300 ml. capacity, which is connected 
to a condenser. By means of a glass tube passing through the 
stopper to the bottom of the retort, a current of dry hydrochloric 
acid is bubbled in. When absorption of the hydrochloric acid 
ceases, the chlorosulphonic acid formed is distilled. The distillate 
is generally slightly coloured ; it may be purified by a further 
distillation. The yield is almost theoretical. 

Industrially, chlorosulphonic acid is prepared by a similar 
method, that is, by bubbling a current of dry gaseous hydrochloric 
acid through a solution of sulphur trioxide in sulphuric acid to 
saturation and separating the chlorosulphonic acid by distillation. 
Or more simply, it may be prepared by the direct reaction 
between hydrochloric acid and sulphur trioxide. 

During the war large quantities were obtained as a by-product 
in the preparation of phosgene from carbon tetrachloride and 
oleum (see p. 61). 

Physical and Chemical Properties 

It is a colourless liquid which boils at 153° to 156° C. with 
partial decomposition. On heating to 158° C, however, it 
decomposes into sulphuric acid, chlorine and sulphur dioxide : 



SO a + HCl = SO ; 




SO. 



•2 





CI 



OH 



H 2 S0 4 + S0 2 + Cl 2 



1 Beckurts and Otto, Ber., 1878, 11, 2058. 



CHLOROSULPHONIC ACID: PROPERTIES 257 



It has a specific gravity of 1776 at 18° C. On cooling strongly 
it solidifies to a mass melting at — 81° C. 

Its heat of formation from sulphur trioxide and hydrochloric 
acid is 14,400 calories, its heat of solution in water is 40,300 
calories, and its heat of volatilisation is 12,800 calories per gm. 
molecule. It has a vapour density of 4-0. 

It fumes in contact with air, forming sulphuric acid and 
hydrochloric acid : 

/CI 

S0 2 ( + HjO = H 2 S0 4 -1- HC1 
N OH 

When hydrogen sulphide acts on chlorosulphonic acid, even in the 
cold, sulphur is formed and hydrochloric acid evolved. 

By the action of chlorosulphonic acid on methyl alcohol at 
— 5 0 C, methyl sulphuric acid is formed (see p. 261), 

/CI /OCH3 
CH 3 -OH + S0 2 ( = HC1 + S0 2 ( 

x OH N OH 

and this by the action of a further molecule of chlorosulphonic 
acid is converted into methyl chlorosulphonate 1 (see p. 266). 

/OH /OCH 3 /OCH3 

S0 2 ( + S0 2 ( = S0 2 ( + H 2 S0 4 

X C1 \)H N C1 

On heating formaldehyde to about 70° C. with chlorosulphonic 
acid, dichloromethyl sulphate and also dichloromethyl ether are 
formed 2 : 



/CI /OCH 2 Cl 
CH 2 0 + S0 2 ( = S0 2 < 

N OH \)H 

/OCH 4 Cl _ /OCH 2 Cl 



2 S0 2 ( * -> S0 2 ( 

N OH x OCH 2 Cl 

Dichloromethyl sulphate is a colourless liquid, with b.p. 
96° to 97° C. at 14 mm. mercury pressure and S.G. i-6o at room 
temperature. It is readily soluble in the common organic 
solvents, though sparingly soluble in petroleum ether. Unlike 
dimethyl sulphate it has no toxic power (see p. 266). 

1 R. Lbvaillant and L. Simon, Compt. rend., 1919, 169, 140. 

2 Fuchs and Katscher, Ber., 1927, 60, 2292. 



WAR GASES. 



258 SULPHUR COMPOUNDS 

Chlorosulphonic acid also reacts with dimethyl sulphate to form 
methyl chlorosulphonate 1 : 

/OH /OCH 3 /OCH s /OCH 3 

S0 2 ( + S0 2 ( = S0 2 < 4- SCU 

N C1 N OCH 3 X C1 N OH 

It reacts with monochloromethyl chloroformate, forming 
monochloromethyl chlorosulphonate 2 : 

/OH /OCH 2 Cl /OCH 2 Cl 

S0 2 ( + CO< = S0 2 < + HC1 + C0 2 

N C1 N C1 Yl 

a colourless liquid, boiling at 49° to 50 0 C. at a pressure of 14 mm. 
mercury and having a density of 1-63 at room temperature. It 
is sparingly soluble in water with partial decomposition. It is 
soluble in the common organic solvents. It strongly irritates 
the mucous membranes (Fuchs and Katscher) . 

The lethal concentration for man at 30 minutes' exposure is 
6,000-8,000 mgm. chlorosulphonic acid per cu. m. of air 
(Lindemann). 

2. Sulphuryl Chloride (M.Wt. 135) 

y Cl 

X C1 

Sulphuryl chloride was chiefly prepared during the war for the 
manufacture of methyl and ethyl chlorosulphonates, but was 
occasionally employed also in admixture with cyanogen chloride, 
phosgene or chloropicrin (Prentiss). 

Preparation 

It may be obtained by heating chlorosulphonic acid to 180° C. 
under pressure. The following reaction takes place : 

/OH /OH /CI 

2 S0 2 ( -> S0 2 ( + S0 2 ( 
X C1 N OH X C1 

In the presence of suitable catalysts, such as salts of mercury, 
this reaction may be carried out at lower temperatures : at 
about 70 0 C. and ordinary pressure. 

1 R. Levaillant and L. Simon, Compt. rend., 1919, 169, 234 ; C. Boulin, 
Compt. rend., 1919, 169, 338. 

* Kraft and Alexejev, J. Obscei Khim., Ser. A., 1932, 2, 728. 



SULPHURYL CHLORIDE 



259 



However, in the laboratory it is more convenient to prepare 
it by synthesis from chlorine and sulphur dioxide : 

S0 2 + Cl a = S0 2 C1 2 , 

in presence of camphor 1 or activated carbon. 2 

10 gm. camphor are placed in a flask of about 500 ml. capacity 
fitted with a reflux condenser which is connected to an aspirator. 
A glass tube with a three-way cock leads to the bottom of the 
flask, which is cooled with iced water while a current of sulphur 
dioxide, dried by means of sulphuric acid, is passed in. The gas 
is rapidly absorbed by the camphor, and when this is reduced to 
a liquid the gas is discontinued and a current of dry chlorine 
bubbled through. When the chlorine is no longer absorbed and 
its colour no longer disappears, it is replaced by sulphur dioxide 
and then chlorine is again passed in. 

When the flask contains 30-40 ml. liquid, both gases are 
passed in together, with external cooling, and when sufficient 
liquid has been produced, the mixed-gas current is stopped and 
the product distilled, collecting the fraction passing over between 
68° to 70° C, which consists of sulphuryl chloride. 

Physical and Chemical Properties 

Sulphuryl chloride is a colourless liquid boiling at 69-2° C. and 
melting at — 54-1° C. Its specific gravity at o° C. is 1708 and 
at 20° C. 1-667. 

Its vapour density is 4-6 and its heat of volatilisation 524 
calories. 

Sulphuryl chloride is slowly decomposed by cold water, but 
hot water or alkalies act rapidly and vigorously, sulphuric acid 
and hydrochloric acid being formed. 3 When sulphuryl chloride 
vapour is passed through a tube heated to dull redness, decomposi- 
tion takes place with formation of sulphur dioxide and chlorine. 

Gaseous ammonia reacts with sulphuryl chloride to form 
ammonium chloride and sulphamide 4 : 

/NH a 

S0 2 CL + a NH. = S0 2 ( + 2 NH 4 C1 

NH 2 

Sulphamide forms white crystals, melting at 92° C. and soluble 
in water. 

1 Schulze, /. prakt. Chem., 1881, [2] 24, 168. 

a Danneel, Z. angew. Chem., 1926, 39, 1553 ; Meyer, Z. angew. Chem., 1931, 
44, 41. 

» Carrara and Zoppellari, Gazz. chim. ital., 1894, 24, 364. 
* Ephraim, Ber., 1910, 43, 146. 

9—2 



2 6o SULPHUR COMPOUNDS 

Iodine in the presence of aluminium chloride reacts with 
sulphuryl chloride in several ways : to form iodine monochloride 
if the sulphuryl chloride is insufficient : 

S0 2 C1 2 + I, = 2ICI + S0 2 ; 

or if the sulphuryl chloride is in excess, to form iodine trichloride : 

3 S0 2 C1 2 + I 2 = 2ICI3 + 3 so 2 . 

By the action of hydriodic acid on sulphuryl chloride sulphur 
dioxide, hydrochloric acid, sulphur and iodine are formed. 1 

On heating to 200 0 C. with sulphur, sulphur monochloride and 
dichloride are formed. This reaction takes place at ordinary 
temperatures in presence of aluminium trichloride. 

Sulphuryl chloride usually behaves as a chlorinating agent. 
For instance, with * benzene chlorobenzene is formed ; with 
acetone mono- and di- chloroacetones ; with aniline trichloro- 
aniline, etc. 

It reacts with methyl alcohol, forming various products 
according to conditions. 2 Thus in presence of excess sulphuryl 
chloride, methyl chlorosulphonate is produced (see p. 266) : 

/OCH 3 

S0 2 C1* + CH3OH =» SO,^ 4- HC1 

In presence of excess of the alcohol, methyl sulphate is formed : 

/OCH g 

2 CH 3 OH + S0 2 C1 2 = S0 2 < + 2 HC1 

x OCH 3 

or else methyl chloride and methyl sulphuric acid : 



OCH. 



3 CH3OH + S0 2 C1 2 = 2 CH3CI + S0 2 < ~ " 3 + H 2 0 

N OH 

It also reacts with ethylene chlorohydrin, forming chloroethyl 
chlorosulphonate 3 : 

/0CH 2 CH 2 C1 

S0 2 Cl a + Cl-CH 2 -CH 2 OH = S0 2 ( ci + HC1 

a liquid boiling at 101 0 C. at a pressure of 23 mm. and having a 

1 Besson, Compt. rend., 1896, 122, 467. 

2 R. McKee, U.S. Pat. 1641005/1927. 

3 W. Steinkopf and coll., Ber., 1920, 53, 1144 '. R - Levaillant, Compt. rend. 
I928, 187, 730. 



METHYL SULPHURIC ACID 



261 



density of 20° C. of 1-552. It is stable during storage and has, an 
odour like that of chloropicrin ; it causes lachrymation. 

On continuing the heating, the reaction proceeds further and 
/?/?' dichloroethyl sulphate is formed 1 : 

CH 2 OH /OCH.CHX1 
2 I + S0 2 C1 2 = S0 2 ( + 2 HC1 

CH 2 C1 ' N 0CH 2 CH 2 C1 

This is a colourless, inodorous liquid which distils without 
decomposition only under reduced pressure. The boiling point is 
154° C. at 8 mm. mercury pressure. Its S.G. at 20 0 C. is 1-4622. 
On cooling it forms a crystalline mass, melting at n°C. and 
insoluble in water. It is hydrolysed neither by water nor 
ammonia. 

Liquid sulphuryl chloride has a slight corrosive action on iron, 
but is without action on lead. 

3. Methyl Sulphuric Acid (M.Wt. 112) 

/OCH3 

so 2 < 

x OH 

The importance of this compound as a war gas is almost nil ; 
it had a very limited use during the war mixed with dimethyl 
sulphate. 

Preparation 

In the laboratory it is prepared by the action of methanol on 
chlorosulphonic acid. According to Claesson, 2 the chlorosulphonic 
acid is placed in a small flask, which is fitted with a tap-funnel 
and externally cooled with ice. Water-free methyl alcohol, 
previously distilled from lime, is slowly introduced in quantity 
stoichiometrically equivalent to the chlorosulphonic acid. As 
each drop of alcohol comes into contact with the chlorosulphonic 
acid, hydrochloric acid is evolved. At the end of addition of the 
alcohol the flask is heated gently while a current of dry air is 
passed through in order to remove the hydrochloric acid dissolved 
in the mixture. The product obtained contains about 90% methyl 
sulphuric acid. 

Physical and Chemical Properties 

Methyl sulphuric acid is an oily liquid which may be cooled 
to — 30° C. without solidifying. On heating to 130° to 140° C. it 

1 Nekrassov and Komissarov, /. prakt. Chem., 1929, 123, 160 ; R. 
Levaillant, Compt. rend., 1928, 187, 730. 

» Claesson, /. prakt. Chem., 1879, [2] 19, 240. 



262 SULPHUR COMPOUNDS 

decomposes almost quantitatively into dimethyl sulphate and 
sulphuric acid : 

/OCH 3 /OCH3 /OH 

2 S0 2 < S0 2 ( + S0 2 < 

N OH N OCH s N OH 

It is sparingly soluble in water and alcohol. In anhydrous 
ether it dissolves in all proportions. 

It reacts with methyl chloroformate to form dimethyl sulphate 
in good yield 1 : 

/OCH3 CI /OCH3 
S0 2 ( + I = S0 2 ( + HC1 + C0 2 

N OH COOCH3 N OCH 3 

With monochloromethyl chloroformate it reacts to form methyl 
chlorosulphonate 2 : 

/OCH3 CI /OCH3 
S0 2 ( + I = S0 2 ( -t- HC1 + C0 2 + CH 2 0 

N OH COOCH 2 Cl X C1 

4. Dimethyl Sulphate (M.Wt. 126-12) 

so 2 < 

x OCH 3 

Dimethyl sulphate was used by the Germans mixed with 
methyl chlorosulphonate, this being the product obtained in the 
industrial manufacture from methanol and chlorosulphonic acid 
when the esterification is incomplete. Dimethyl sulphate mixed 
with chlorosulphonic acid was used by the French under the name 
of " Rationite." 

Dimethyl sulphate, before being employed as a war gas, was 
used in industry as a methylating agent for amines and phenols. 
In recent years it has also been employed as a catalyst in the 
preparation of cellulose esters. 3 

Preparation 

It may be obtained by the decomposition of methyl sulphuric 
acid at high temperatures and in vacuo : 

/OCH3 /OCH3 /OH 

2 S0 2 ( -> S0 2 ( + S0 2 ( 

\>H N OCH 3 N OH 

1 M. Kraft and F. Ljutkina, /. Obscei Khim., Ser. A., 1931, 1, 190. 

2 M. Kraft and B. Alexejev, /. Obscei Khim., Ser. A., 1932, 2, 726. 
* Brit. Pat. 306531/1929. 



DIMETHYL SULPHATE: PREPARATION 263 



or by the action of methyl alcohol on sulphuryl chloride : 

/CI HOCH3 /OCH3 
SOA + = S0 2 ( + 2 HC1 

N C1 HOCH3 N OCH 3 

or else by the esterification of fuming sulphuric acid with methyl 
alcohol : 

/OH HOCH 3 /OCH, 
SO a < + v = S0 2 < + 2 H 8 0 
N OH HOCH 3 \)CH 3 

Guyot and Simon, 1 employing oleum containing 60% S0 3 in 
the last method have obtained a very high yield of dimethyl 
sulphate (about 90%). 

Recently a method of preparation has been worked out based 
on the reaction between methyl nitrite and methyl chloro- 
sulphonate 2 : 

/OCH s /OCH3 
SO a < 4- ON • OCH3 = S0 2 ( + NOC1 

N C1 X OCH 3 

Laboratory Preparation 

In the laboratory it is preferable to prepare dimethyl sulphate 
by Ullmann's method, 3 that is, by the action of methyl alcohol 
on chlorosulphonic acid. 

100 gm. chlorosulphonic acid are placed in a 200 ml. distillation 
flask which is closed with a rubber stopper containing two holes. 
Through one of the holes passes a thermometer and through the 
other a tap-funnel of the " Bulk " type 4 containing 27 gm. 
water-free methyl alcohol. The exit tube of the distillation flask 
is connected with a wash-bottle containing a little sulphuric acid, 
and the exit from this leads to a second bottle partly filled with 
water which serves to absorb the hydrochloric acid formed in the 
reaction. 

The contents of the flask are cooled to — 10° C. by means of a 
freezing mixture and then the methyl alcohol allowed to enter 
from the tap-funnel, regulating the rate of addition so that the 
evolution of hydrochloric acid is not too violent. During the 
addition of the alcohol, the contents of the flask are repeatedly 

1 Guyot and Simon, Compt. rend., 1919, 169, 795. 
» R. Levaillant, Compt. rend., 1928, 187, 234. 
8 Ullmann, Ann., 1903, 327, 104. 

4 This funnel has a very narrow stem (3-4 mm. diameter) which ends in a long 
capillary bent in a crook for 5-10 mm. at the end. The stem, which should reach 
almost to the bottom of the flask, should be filled with methyl alcohol before the 
reaction commences. 



264 



SULPHUR COMPOUNDS 



agitated and care is taken that the temperature does not rise 
above — 5° C. The whole operation takes about i£ hours. 

When all the alcohol has been added, the product is allowed 
to stand for about 12 hours and then distilled under 20 mm. 
mercury pressure, heating the flask on an oil bath to 140° C. The 
distillate consists of almost pure dimethyl sulphate, and is finally 
washed with a little cold water and dried with calcium chloride. 
Yield is 80% of theory. 

Industrial Manufacture 

Industrially, dimethyl sulphate is nowadays prepared almost 
exclusively by the action of chlorosulphonic acid on methyl 
alcohol at a low temperature in the presence of carbon tetra- 
chloride and then distillation of the product at reduced 
pressure. 

6-4 kg. 99% methanol are placed in an enamelled iron vessel 
fitted with a reflux apparatus, together with 20 kg. carbon 
tetrachloride, and then 24 kg. chlorosulphonic acid are added 
slowly while stirring. At the end of this operation, the carbon 
tetrachloride is first distilled off on a water-bath and collected 
for employment in another preparation, and then the dimethyl 
sulphate is distilled under reduced pressure. 1 

Physical and Chemical Properties 

Dimethyl sulphate is a colourless, inodorous liquid which boils 
at ordinary pressure at 188° C. with partial decomposition, while 
at 15 mm. of mercury pressure it boils without decomposition 
at 96° C. It solidifies at — 317 0 C. 2 and has a specific gravity of 
I- 333 at 15° C. Its vapour density is 4-3. Its volatility at 20 0 C. 
is 3,300 mgm. per cu. m. According to this, dimethyl sulphate is 
unsuitable for use as an asphyxiant war gas because its volatility 
is too low and equally unsuitable as- a vesicant because its 
volatility is too high. 

Dimethyl sulphate is sparingly soluble in water (about 2-8%), 
but soluble in the common organic solvents. 

It is decomposed by alkalies and partially even by cold 
water 3 : 



so/ 



<OCH. 



'3 




•OCH3 



OCH3 



OH 



+ CH s OH 



1 Soc. prod. chim. Fontaines (Lyons), D.R.P., 193830. 
8 Timmerman, Bull, soc. chim. belg., 1921, 30, 62. 
3 Kremann, Monatsh., 1907, 28, 13. 



DIMETHYL SULPHATE: PROPERTIES 265 

Boulin and Simon 1 have observed that on long standing, a 
mixture of water and dimethyl sulphate becomes homogeneous. 
This is attributed to the fact that decomposition takes place as 
follows, in these circumstances : 



The methyl ether formed is completely soluble in the sulphuric acid 
also produced in the reaction. 

Dimethyl sulphate reacts in a similar manner with other 
substances containing the hydroxyl group, such as phenols. 
These compounds condense readily and quantitatively in alkaline 
solution with dimethyl sulphate. According to Ullmann, 2 
dimethyl sulphate may be usefully employed instead of methyl 
iodide for introducing methyl groups into organic molecules. 

It reacts with hydrogen peroxide, forming methyl peroxide, 
CH 3 — O — O — CH 3 , a gas at ordinary temperatures with an odour 
reminiscent of nitrous gases. It boils at 13-5° C. at a pressure of 
740 mm. Heated in admixture with air it explodes with violence 
and flame, evolving formaldehyde. The vapour of methyl 
peroxide irritates the respiratory passages. 3 

Dimethyl sulphate also reacts with amines. For instance, with 
the aromatic primary amines it forms the methyl sulphate of the 
primary amine, together with the corresponding secondary base 
(Ullmann) : 



The tertiary amines in ethereal or benzene solution react with 
dimethyl sulphate, forming quaternary ammonium compounds. 

Dimethyl sulphate does not attack metals. It is only to a 
slight extent absorbed by animal and vegetable fibres ; cotton 
absorbs more than wool. 4 

A normal man cannot breathe the gas for more than one 
minute in concentrations greater than 50 mgm. per cu. m. of air 
(Flury). The mortality-product, determined with cavies, is 
35,ooo. 5 Even at low concentrations it has a vesicant action on 
the skin. 



1 Boulin and Simon, Compt. rend., 1920, 170, 392. 
8 Ullmann, loc. cit. 

3 A. Rieche, Ber., 1928, 61, 951. 

4 Alexejevsky, /. Prikl. Khim., 1929. 1, 184. 

6 G. FERRAROLo, Minerva medica., May, 1936, No. 18. 





OCH s 
OCH3 




R 



CH 3 



2 66 



SULPHUR COMPOUNDS 



5. Methyl Fluorosulphonate (M.Wt. 114) 

/OCH3 

so/ 

X F 

Methyl fluorosulphonate was obtained by Meyer 1 in 1932 by 
the action of fluorosulphonic acid on dimethyl ether : 

CH A /OH /OCH3 

0 + 2 S0 2 < = 2 S0 2 ( -f H 2 0 

ciy X F V 



Laboratory Preparation 1 

10 ml. fluorosulphonic acid are placed in a wash-bottle and a 
current of dry dimethyl ether, obtained by heating 1-3 parts 
methanol with 2 parts concentrated sulphuric acid to 140° C. is 
passed in. The methyl ether is absorbed and reacts immediately. 
For safety, a second wash-bottle should be inserted containing a 
further 10 ml. fluorosulphonic acid, and after this it is best to 
introduce another, containing concentrated sulphuric acid. 2 
After 3 hours, tha is, when the fluorosulphonic acid in the first 
bottle absorbs no "more methyl ether, the product is distilled 
under reduced pressure. At a pressure of 160 mm. methyl 
fluorosulphonate distils at 45 0 C. 



Physical and Chemical Properties 

Methyl fluorosulphonate is a liquid with an ethereal odour, 
boiling at 92° C. at ordinary pressure. It has a specific 
gravity of 1-427 at 16° C, and attacks glass. In the cold it 
has very little attack on rubber, cork and other organic 
substances. 

It is not miscible with water, but is rapidly saponified, especially 
in the presence of alkalies or acids. 
It has toxic properties (Meyer). 

6. Methyl Chlorosulphonate (M.Wt. 130 55) 

/OCH3 
SO/ 
X C1 

Methyl chlorosulphonate was employed by the Germans both 
alone, and in admixture with dimethyl sulphate (75 parts 
dimethyl sulphate and 25 parts methyl chlorosulphonate) under 
the name of " C-Stoff." 

1 J. Meyer and G. Schramm, Z. anorg. Chem., 1932, 206, 27. 

2 E. Erlenmeyer, Ber., 1874, 7, 699. 



METHYL CHLOROSULPHONATE 



267 



Preparation 

The usual method of preparing this war gas is by the action of 
methyl alcohol on sulphuryl chloride 1 : 



65 gm. sulphuryl chloride are placed in a flask of 150-200 ml., 
which is fitted with a dropping funnel and a reflux condenser 
connected at its upper end by a tube to a flask filled with water. 
The function of the water in the flask is to trap the hydrochloric 
acid which is evolved in the reaction. 15 gm. methyl alcohol 
(preferably dried) are allowed to drop in slowly from the tap- 
funnel. During this addition the reaction mixture is agitated 
continuously and the flask is cooled externally with ice. When 
all the alcohol has been added, the flask is allowed to stand for 
2-3 hours and then heated to 50 0 to 6o° C. on the water-bath, 
until all the hydrochloric acid has been evolved. The liquid 
product is then placed in a separatory funnel, washed rapidly 
with iced water and the heavier layer separated and distilled in 
vacuo, the fraction boiling between 38 0 and 45 0 C. at 16 mm. 
pressure being collected. 

Physical and Chemical Properties 

It is a colourless liquid with a pungent odour and boils at 
ordinary pressure at 133° to I35°C. with decomposition. At 
16 mm. pressure it distils unaltered at 42 0 C. It melts at — 70 0 C. 
and has a S.G. at 15° C. of 1-492, while its vapour density is 4-5 
(air = 1). The volatility at 20° C. is 60,000 mgm. per cu. m. It is 
immiscible with sulphuric acid, 2 but miscible with carbon tetra- 
chloride, chloroform and ethyl alcohol. It is insoluble in water, 
which hydrolyses it according to the equation : 



That is, unlike the sulphuric esters, methyl sulphuric acid 
and dimethyl sulphate, it does not split off its alkyl group on 
hydrolysis, but only the chlorine atom. 

If the water is in excess, however, even the methyl sulphuric 
acid which is formed is decomposed into hydrochloric acid and 
methyl alcohol. 3 

1 Behrend, /. prukt. Chem., 1877, [2] 15, 32. 

2 R. Levaillant and L. Simon, Compt. rend., 1919, 169, 140. 
s L. Guyot and L. Simon, Compt. rend., 1920, 170, 326. 




+ HCl 




268 SULPHUR COMPOUNDS 

It reacts with methyl nitrite at about 140 0 C, forming dimethyl 
sulphate 1 : 

/OCH3 /OCH 3 
S0 2 < + ON • OCH3 = S0 2 ( + NOC1 



X C1 x OCH. 



3 



The minimum concentration capable of provoking irritation is 
2 mgm. per cu. m. of air (Miiller). The limit of insupportability 
according to Lindemann is 30-40 mgm. per cu. m. Mortality- 
product : 2,000 (Miiller). 

7. Ethyl Chlorosulphonate (M.Wt. 144-57) 

/OC 2 H 5 
S0 2 < 
X C1 

This compound was used by the French, at the suggestion of 
Grignard, towards the end of 1915, because of its irritating action 
on the skin. It was also employed mixed with bromoacetone. 

Preparation 

It is generally prepared by the reaction of ethylene with 
chlorosulphonic acid in the cold 2 : 

/OH /OC 2 H 5 
C 2 H 4 + S0 2 ( ci =S0 2 ( Q 

It may also be obtained by the action of fuming sulphuric acid 
on ethyl chloroformate. 3 

Physical and Chemical Properties 

Ethyl chlorosulphonate is a colourless, oily liquid fuming in 
damp air and having a pungent odour. It boils at ordinary 
pressure at 152 0 to 153° C. and at 100 mm. pressure at 93 0 to 95 0 C. 
Its specific gravity at 0° C. is 1-379, and its vapour density is 
five times that of air. It has a low vapour pressure. 

It is insoluble in water and is readily decomposed by cold water 
according to the equation : 

/OCH, /OC.H5 
S0 8 ( + HOH = SO s ( 4- HC1 

N C1 *\)H 

That is to say, it gives up the chlorine atom and not the alkyl 

1 R. Levaillant, Compt. rend., 1928, 187, 234. 
8 Muller, Ber., 1873, 6, 228. 
» Wilm, Ber., 1873, 6, 505. 



SULPHURIC ACID DERIVATIVES : ANALYSIS 269 



group on hydrolysis, like the methyl derivative already described. 
However, the velocity of hydrolysis is lower. 

It dissolves readily in ligroin, chloroform and ether. 1 On 
heating to about 160° C. it decomposes to form sulphur dioxide, 
sulphuric acid, hydrochloric acid and ethylene. 2 

When treated with aniline dissolved in ether, it forms ethyl 
chloride and sulphanilic acid. 

Ethyl chlorosulphonate does not attack iron or steel, but 
attacks copper slightly and lead and tin vigorously. 

The lower limit of irritation is the same as that of the methyl 
derivative, that is, 2 mgm. per cu. m. of air (Miiller). The limit 
of insupportability, according to Flury, is 50 mgm. per cu. m. and 
the mortality-product is 3,000 (Muller) and 10,000 (Prentiss). 

Analysis of the Sulphuric Acid Derivatives 

Detection 

The detection of these compounds is usually carried out by 
utilising their reaction with alkaline solutions or sometimes with 
water alone, in which sulphuric acid, hydrochloric acid, methyl or 
ethyl alcohol, etc., are formed. These may then be recognised 
by the usual methods of qualitative analysis. 

Detection of Chlorosulphonic Acid. This substance may be 
detected by absorbing a sample in sodium hydroxide solution and 
then testing for the presence of chloride with silver nitrate 
and of sulphate with barium chloride. 

Detection of Sulphuryl Chloride. According to Heumann and 
Kochling, 3 when gaseous sulphuryl chloride is passed through a 
glass tube raised to dull red heat, decomposition takes place as 
follows : 

S0 2 C1 2 = S0 2 + Cl 2 . 

By testing for chlorine and sulphur dioxide in the gas produced, 
it is possible to detect the presence originally of sulphuryl chloride. 
According to the same authorities it is advisable to confirm the 
presence of chlorine by means of potassium iodide and of sulphur 
dioxide with lead dioxide, which becomes white on being 
converted to sulphate. 

Detection of Dimethyl Sulphate.* In order to test for dimethyl 
sulphate, about 2 gm. of the sample are digested in a reflux 
apparatus with 50 ml. water for about 1 hour. The solution is 

1 Bushong, Amer. Chem. Jour., 1903, 30, 214. 

2 Willcox, Amer. Chem. Jour., 1904, 32, 471. 

3 Heumann and Kochling, Ber., 1883, 16, 602. 
1 F. E. Weston, Carbon Compounds, 1927, 95. 



270 



SULPHUR COMPOUNDS 



then distilled ; the distillate is tested for methyl alcohol and the 
residue for sulphuric acid. 

Quantitative Determination 

The quantitative determination of the sulphuric acid deriva- 
tives may be carried out as described in the paragraphs above 
dealing with their qualitative analysis : by decomposing the 
sample by warming with water or alkaline solutions and then 
determining the sulphuric and hydrochloric acids quantitatively. 

Determination of Chlorosulphonic Acid. About 1 gm. of the 
sample is introduced into a small glass bulb which is then sealed 
in the flame and weighed accurately. This bulb is then placed 
in a tall glass cylinder of about 150 ml. capacity, containing 
about 100 ml. water. The cylinder is stoppered tightly and 
shaken violently so as to break the bulb, and then allowed to 
stand until the cloud which first forms in the cylinder completely 
disappears. The contents are then transferred to a 500 ml. flask 
and made up to volume. 200 ml. of the solution are then titrated 
with a decinormal sodium hydroxide solution, to the methyl- 
orange end-point, so as to obtain the total hydrochloric and 
sulphuric acid content. In another 200 ml. the hydrochloric acid 
is titrated with a decinormal solution of silver nitrate in presence 
of a few drops of potassium chromate solution, after addition of 
excess of pure calcium carbonate. 

Calculation : If a gm. sample were taken and b ml. N/10 
sodium hydroxide and c ml. N/10 silver nitrate were employed, 
then 

%HC1 = 2^*i 

%H 2 S0 4 = I -°°° 75 /~ C) 

Determination of Sulphuryl Chloride. 1 A simple method of 
determining this substance is based on its quantitative decomposi- 
tion into chlorine and sulphur dioxide when it is passed through 
a tube heated to dull-redness (see p. 259). Then on determining 
the chlorine and the sulphur dioxide by one of the ordinary 
methods, the amount of sulphuryl chloride present in the sample 
may be deduced. 

1 Private communication from Dr. Rusberg (Lunge-Berl, Chem. Techn. 
Untersuchungsmethoden, 7th edition, 1921, 877). 



CHAPTER XV 



ARSENIC COMPOUNDS 

Towards the end of the war of 1914-18, the attention of 
chemists searching for new war gases returned to the arsenic 
compounds which had already frequently been considered, on 
account of their great toxicity. Only a few had actually been 
employed, however, for their physical properties rendered them 
unsuitable in general. Thus all the inorganic compounds were 
discarded, excepting hydrogen arsenide, 1 which was tested at the 
commencement, but was also abandoned because of its instability 2 
and rapid diffusion 3 and arsenic trichloride, which had only a 
limited employment and that solely as solvent for the war gases 
(phosgene, hydrocyanic acid, etc.). 4 

A very large number of potential war gases was found amongst 
the organic derivatives however. The superiority of the organic 
arsenicals over the inorganic compounds is attributed to the fact 
that the former are, in general, soluble in the lipoids and dissolve 
preferentially in lecithin and cephalin, while the inorganic 
compounds are rapidly eliminated via the kidneys and the 
mucus. 5 

From the results of the researches carried out on the organic 
arsenic compounds, it is possible to divide these into the following 
groups : 

(1) Aliphatic Arsines : Methyl dichloroarsine. 

Ethyl dichloroarsine. 
Chlorovinyl arsines. 

(2) Aromatic Arsines : Phenyl dichloroarsine. 

Diphenyl chloroarsine. 
Diphenyl cyanoarsine. 

(3) Heterocyclic Arsine : Phenarsazine chloride. 

Of these, the aromatic arsines were very largely used during 
the war, especially diphenyl chloroarsine. The aggressive action 
of these aromatic arsines, unlike that of all the compounds 

1 Ferrarolo, Gazz. Intern. Medicina e Chirurgia, 1936. 

2 Nekrassov, Khimija Otravliajuscikh Vescestv, Leningrad, 1929, 145. 

3 Mihai Cristea, Antigaz, 1931. Nos. 9-10. 

4 Lustig, Policlinico, March, 1935- 

6 Hofmann, Sitzb. kgl. preuss. Akad. Wiss., 1935, 24, 447. 

271 



272 



ARSENIC COMPOUNDS 



described previously, is provoked by finely divided solid particles, 
which on liberation in the air form true smokes and are known as 
the " toxic smokes." Phenyl dichloroarsine is an exception, not 
being a smoke. 

Most of the aliphatic and aromatic arsines employed during 
the war of 1914-18 were substances which had been known for 
some time. The only new substances are the chlorovinyl arsines 
and phenarsazine chloride, of whose practical efficiency somewhat 
conflicting opinions are still held. 

The fact that during the war only the compounds mentioned 
above were actually used does not indicate that they were 
superior to others which have been prepared and studied. 
Nevertheless, it is probable that preference will be given to those 
substances whose range of application is known, without using 
compounds of uncertain scope. 

(A) ALIPHATIC ARSINES 

The aliphatic arsines are substances which are generally liquid 
and oily, have a not unpleasant odour, are somewhat miscible with 
water, but are all more or less rapidly hydrolysed as follows : 

/CI H\ 
R-As< + )0 = R-AsO + 2 HC1 
N C1 H' 

These substances, though more powerfully toxic than the 
aromatic arsines, are of minor importance because of their rapid 
diffusion in the air without forming aerosols. 

Even the chlorovinyl arsines, although they are easily prepared, 
do not seem to be sufficiently aggressive in their action to replace 
the aromatic arsines. According to several authorities, 1 experi- 
ments on the methods of military application of the chlorovinyl 
arsines have been abandoned even in America. 

Of the aliphatic arsines, only ethyl dichloroarsine has been 
widely employed as a war gas and is considered as the typical 
substance for use in projectiles. Methyl dichloroarsine is classed 
by some German authors 2 as a substance which was studied in 
the post-war period, but according to an American authority it 
was actually employed by the Allies towards the end of the war, 
though only in small quantity. 3 

Since the war, various other compounds of similar properties 
and method of preparation have been prepared and studied. 

1 Hanslian, Der Chemische Krieg, Berlin, 1927, 62. 

2 U. Muller, Die Chemische Waffe, Berlin, 1932, m. 

s Fries and West, Chemical Warfare, New York, 192 1, 181. 



METHYL DICHLOROARSINE : PREPARATION 273 

For instance, dimethyl chloroarsine (b.p. 106-5° to 107° C), 
dimethyl bromoarsine 1 (b.p. 128° to 129° C), dimethyl fluoro- 
arsine, 2 methyl dicyanoarsine 3 (m.p. 115-5° to ii6 - 5°C.), ethyl 
dibromoarsine, etc. All of these have aggressive properties 
inferior to those of methyl dichloroarsine. 

Homologues of methyl dichloroarsine have also been prepared : 

n-Butyl-dichloroarsine* QHgAsOa, obtained by the action of 
hydrochloric acid on w-butyl arsenic acid in the presence of 
sulphur dioxide, is an oily liquid boiling at 192° to 194° C. 

Iso-amyl dichloroarsine^ C 6 H n AsCl 2 , obtained by the action of 
phosphorus trichloride on iso-amyl arsenic acid, is a liquid boiling 
at 88-5° to 91-5° C. at 15 mm. mercury pressure. 

This latter substance has great irritant power (Liebermann) . 

1. Methyl Dichloroarsine (M.Wt. 161) 

CI 

CHa ~ As \ci 

Methyl dichloroarsine was prepared by Bayer 6 in 1858 by two 
different methods : 

(a) By the decomposition of cacodyl trichloride at 40° to 50° C. 

Cl\ /CH 3 /CI 

Cl-As( CH 3 As( + CHgCl 

CI/ N CH 3 N C1 

(6) By the action of gaseous hydrochloric acid on cacodylic 
acid 7 : 

CH 3 \ /CI 

^AsOOH + 3 HCl = CH 3 -As^ + CH 3 C1 + 2 HjO 
CH 3 CI 

Methyl dichloroarsine may also be obtained by treating 
dimethyl arsine with chlorine 8 : 

CH.\ /CI 

>As-H + 2 Cl 2 = CH a As< + CH3CI + HCl 
CH/ CI 

1 Steinkopf and Schwen, Ber., 1921, 54, 1454. 

2 Bunsen, Ann., 1841, 37, 38. 

8 Gryszkiewicz and Trochimovsky, Bull. soc. chim., 1927, 41, 1323. 

* Quick and Adams, /. Am. Chem. Soc, 1922, 44, 805 ; Hanzlik, /. Pharmoc., 
1919, 14, 221. 

6 Steinkopf and Mieg, Ber., 1920, 53, 1015. 

• Bayer, Ann., 1858, 107, 269. 

7 Zappi and coll., Bull. soc. chim., 1928, [4] 43, 1230. 

8 Dehn and Wilcox, /. Am. Chem. Soc, 1906, 35, 16. 



274 



ARSENIC COMPOUNDS 



or, according to Auger, 1 by bringing about the reaction between 
methyl arsenic acid and phosphorus trichloride, which both 
reduces and chlorinates : 

/OH /CI 
CH 3 -Asf O + PC1 3 -> HPO3 + CH 3 As< + HCl 
\OH N C1 

It is easily understood that this reaction, though convenient 
enough for the laboratory preparation of methyl dichloroarsine, 
is not suitable for its industrial manufacture because of the 
difficulty of procuring large quantities of the raw materials. 
The lack of an easy and simple method of manufacture may be 
considered as one of the principal causes which prevented methyl 
dichloroarsine from being employed as a war gas until the very 
end of the war, when only the Americans succeeded in producing 
it on an industrial scale by a simple method. 

The method used by the Americans 2 commenced with sodium 
arsenite and dimethyl sulphate, and proceeded by the following 
stages : 

(1) Methylation of the sodium arsenite with dimethyl sulphate 3 : 

CH 8 \ CH,\ .ONa 

Na3As0 3 + >S0 4 = >S0 4 + CH 3 As=0 

CH/ Na' ^ONa 

(2) Reduction of the sodium methyl arsenate with sulphur 
dioxide, after acidification : 

/ONa 

CH 3 -Asf O + S0 2 = Na^O, + CH 3 -As=0 
\ONa 

(3) Chlorination of the methyl arsenious oxide with hydrochloric 
acid : 

/CI 

CH 3 As=0 + 2 HCl = CH 3 As< + H,0 

X C1 

Laboratory Preparation 

In the laboratory, methyl dichloroarsine may be prepared by 
the method indicated above. 4 

100 gm. arsenious oxide are placed in a wide-mouthed glass 
flask of 1 litre capacity, a solution of 120 gm. sodium hydroxide 
in 150 gm. water is added and the whole heated on a water-bath 

1 Auger, Compt. rend., 1906, 142, 1151. 

2 Uehlinger and Cook, /. Ind. Eng. Chem., 1919, 11, 105. 

3 D.R.P. 404589/March 15th, 1923. 

4 Nenitzkscu, Antigaz, 1929, No. 2. 



METHYL DICHLOROARSINE : MANUFACTURE 275 



at 80° C. until the arsenious oxide is completely dissolved. 
Then, without heating, but stirring vigorously with a mechanical 
agitator, 64 gm. dimethyl sulphate are added little by little. 
The reaction between sodium arsenite and dimethyl sulphate is 
highly exothermic and the rate of addition of the latter should 
be so regulated that the temperature does not rise above 85° C. 

When all the dimethyl sulphate has been added, the flask is 
fitted with a reflux condenser and the contents boiled for 2 hours. 
The sodium salt of methyl arsenic acid is obtained. It is allowed 
to cool and a small amount of potassium iodide is added, after 
which a current of sulphur dioxide is passed through the liquid 
until it is saturated (about 6 hours) . The mixture is again boiled 
under reflux for about an hour ; during this period, an oily 
substance consisting of methyl arsenious oxide deposits at the 
bottom of the flask, where it is saturated with a current of gaseous 
hydrochloric acid, while the flask is cooled externally. On 
attaining complete saturation, the flask is connected with a 
Liebig's condenser and the liquid distilled. Much hydrochloric 
acid is evolved at first ; later a mixture of hydrochloric acid 
and methyl dichlor oar sine distils over. The distillation is 
continued until no more oily liquid condenses. The distillate is 
placed in a separatory funnel and the oily layer separated and 
distilled. 

Industrial Manufacture 

A diagram of the American plant for the manufacture of methyl 
dichloroarsine is shown as Fig. 15. 

The reaction takes place in a Pfaudler kettle A of about 100 
gallons capacity, which is double-walled to allow of steam- 
heating and fitted with a mechanical agitator F. At the top of the 
lid two three-way cocks R and R' are fitted. The cock R serves 
for the introduction of the reactants and is connected with a long 
leaden tube which reaches almost to the bottom. This cock also 
connects both with the receiver C containing sodium arsenite, 
and with the two cylinders DD' of sulphur dioxide, with a pipe 0 
through which the dimethyl sulphate enters and also with a smaller 
Pfaudler vessel B, of about 50 gallons capacity, in which the 
hydrochloric acid is prepared. The sulphuric acid which is used 
for preparing the hydrochloric acid is contained in the vessel G 
which is fed from the storage vessel E by means of a pump. 

The three-way cock R' serves to carry off the reaction products 
and leads one way to a water-cooled condenser M and the other 
to a reflux condenser P, consisting of a lead coil contained in an 
iron cylinder full of ice and water, and leading to two sight 



276 



ARSENIC COMPOUNDS 



bottles, / and L, by means of which any escape of gas from the 
apparatus may be observed. 

A solution of sodium arsenite is first prepared in the container C 
by dissolving 42 kg. arsenious oxide in a solution of 64 kg. of 
NaOH in 188 kg. water. When it has completely dissolved the 
solution is introduced into the Pfaudler kettle A and then 64 kg. 
methyl sulphate are added through the pipe 0, maintaining the 
temperature at about 85 0 C. The completion of the conversion 




Fig. 15. 



of the sodium arsenite into sodium methyl arsenate is shown by 
a drop in temperature. When this reaches 50° to 55 0 C. a current 
of sulphur dioxide is introduced from the cylinders D and D' and 
bubbles through the reaction product, which is maintained at 
65° C, until complete saturation is attained and the reduction to 
methyl arsenious oxide complete. A current of gaseous hydro- 
chloric acid is then passed in through the cock R to complete 
saturation, and finally the mixture is distilled. 

The distillate is collected in a separatory vessel, and the oily 
layer dried with calcium chloride and fractionally distilled from 
an oil-bath. The methyl dichloroarsine passes over between 
129 0 and 133 0 C. 

Physical and Chemical Properties 

Methyl dichloroarsine is a mobile, colourless liquid which has a 
characteristic odour and does not fume in the air. 



METHYL DICHLOROARSINE : PROPERTIES 277 



It boils at 37 0 C. at 25 mm., 1 at 55-5° C. at 50 mm., 2 at 72-1° C. 
at 100 mm., 2 at 89-1° C. at 200 mm. 2 and at 132 0 to 133 0 C. at 
ordinary pressure. Its melting point is — 42*5° C. (Gibson) and 
its specific gravity 1-838 at 20° C. It has a vapour density of 5-5 
and a coefficient of thermal expansion of 0-00102. 

The vapour tension at a temperature t may be calculated from 
the formula (see p. 5). 

log^ = 8-6944 -Jf^? 

The values of the vapour tension at the following temperatures 
are 8 : 

TEMPERATURE VAPOUR TENSION 

0 C. mm. mercury 

— 1.5 0-67 

o 2-17 

15 5'94 
25 10-83 

35 i9'33 

The volatility of methyl dichloroarsine at 20° C. is 74,440 mgm. 
per cu. m. of air. 

It dissolves in water (1 gm. in 1,000 ml. water), being rapidly 
hydrolysed according to the equation 4 : 

CH 3 AsCl 2 + H 2 0 = CH 3 AsO + 2HCI. 

It is, however, easily soluble in the common organic solvents. 

In contact with alkaline solutions, methyl dichloroarsine is 
quantitatively decomposed : 

CH 3 AsCl 2 + 2NaOH = CH 3 AsO + 2NaCl + H 2 0, 

forming methyl arsenious oxide, as with water. This oxide is 
crystalline and colourless, has an odour of asafoetida and melts 
at 95° C. Its density is 2-48 and it is soluble in water, alcohol, 
ether and benzene and readily volatile in steam. 5 

Solutions of methyl dichloroarsine in carbon disulphide when 
cooled to — io° C, easily absorb chlorine forming large crystals 
of methyl tetrachloroarsine, which decompose at 0° C. into methyl 
chloride and arsenic trichloride 6 : 

CH 3 AsCl 2 + Cl 8 CH^s — Cl 4 -+ CH3CI + AsCl 3 . 

1 Herbst, Kolloidchem. Beihefte, 1926, 23, 313. 
• Gibson and Johnson, /. Chem. Soc, 1931, 2520. 

3 Baxter and Bezzenberger, /. Am. Chem. Soc, 1920, 42, 1386. 

4 Adams, Private communication ; Raiziss and Gavron, Organic Arsenical 
Compounds, New York, 1923, 41. 

s Raiziss and Gavron, op. cit. 
« Bayer, Ann., 1858, 107, 281. 



278 



ARSENIC COMPOUNDS 



Methyl dichloroarsine reacts with bromine water, forming 
methyl arsenic acid : 

CH 3 As-Cl 2 + H 2 0 = CH 3 AsO + 2 HC1 
CH,AsO + 2 H 2 0 + Br 2 = CH 3 AsO-(OH) 2 + 2 HBr 

Methyl arsenic acid forms acicules with a melting point of 
159 0 C. It is also obtained by the action of hydrogen peroxide 
on methyl dichloroarsine. 1 

Like all the halogenated arsines, gaseous ammonia converts it 
quantitatively into methyl arsinimide, 2 CH 3 As=NH. This 
forms crystals which have an irritating odour and vesicant power 
and melt at 205° C. 

In dry ether solution, methyl dichloroarsine does not react 
with magnesium, though in presence of water the reaction is 
violent : methyl arsine, hydrogen, methane and a compound, 
(CH 3 As) x , are formed. Zinc reacts similarly. 3 

With hydrogen sulphide, methyl arsenious monosulphide is 
formed (Bayer) : 



This compound forms acicular crystals or small prisms with 
melting point 110° C. A detection reaction for the primary 
arsines is based on this sulphide formation 4 (see p. 328). 

Aqueous solutions of methyl dichloroarsine reduce ammoniacal 
silver nitrate solutions (Nametkin) . 

Methyl dichloroarsine reacts with acetylene in presence of 
anhydrous aluminium chloride, forming a mixture of 5 : 

(i) £ chlorovinyl methyl chloroarsine of the formula 



This is a liquid with a boiling point of 112° to 115° C. at 10 mm. 
mercury pressure, which behaves chemically in a similar manner 
to methyl dichloroarsine. It has a lesser irritant power, but has 
a vesicant action on the skin, producing blisters which are 
difficult to heal. 

1 Backer and coll., Rec. trav. Chim., 1935, 54, 186. 

2 Ipatiev and coll., Ber., 1929, 62, 598. 
8 Zappi, Bull. soc. chim., 1918, 23, 322. 

* S. Nametkin and W. Nekrassov, Z. anal. Chem., 1929, 77, 285. 

* Das Gupta, J. Ind. Chem. Soc, 1936, 13, 305. 



CH 3 AsCl 2 + H 2 S = CH 3 AsS + 2HCI. 




ETHYL DICHLOROARSINE : PREPARATION 279 

(ii) /?/?' dichlorovinyl methylarsine 

/CH=CHC1 
CH 3 -As( 

N CH=CHC1 

a liquid, with b.p. 140° to 145° C. at 10 mm. mercury pressure, 
having physiopathological properties similar to the preceding. 

Dry methyl dichloroarsine does not attack iron or zinc 
(Prentiss). 

The lower limit of irritation is 2 mgm. per cu. m. of air (Miiller). 
The maximum concentration which a normal man can breathe 
for a period not greater than 1 minute is 25 mgm. per cu. m. of 
air (Lustig). The lethal index is 3,000 according to Miiller and 
5,600 for 10 minutes' exposure according to Prentiss. 

The vapours of these substances have a vesicatory action of the 
same type as that of dichloroethyl sulphide. 1 

2. Ethyl Dichloroarsine (M.Wt. 175) 

n 

C 2 H 5 — As< 

Vi 

Ethyl dichloroarsine was prepared by La Coste 2 in 1881 by 
acting on mercury diethyl with arsenic trichloride : 

/CI 

2 AsCl 3 + Hg(C 2 H 5 ) 2 = 2 C 2 H 5 As<^ + HgCl, 

It may also be obtained by heating ethyl arsine in a closed 
tube with mercuric, arsenic, antimony or stannous chloride. 3 

C 2 H 5 AsH 2 + 2HgCl 2 = C 2 H 5 AsCl 2 + 2 Hg + 2 HC1, 

or by the decomposition of 10 ethyl 5-10 dihydrophenarsazine 
with gaseous hydrochloric acid 4 : 

C 2 H 5 -As( 6 )NH -t- 2 HC1 = C a H 5 AsCl a + (C 6 H 6 ) 2 NH 

Ethyl dichloroarsine was employed in March, 1918, by the 
Germans, being considered suitable for replacing dichloroethyl 
sulphide in offensive operations because of its immediate vesicant 
effect and its non-persistent character. 

1 Hanzlik, loc. cit. 

a La Coste, Ann., 1881, 208, 33. 

3 Dehn, Am. Chem. Jour., 1908, 40, 88. 

4 Gibson and Johnson, /. Chem. Soc, 1931, 2518. 



28o 



ARSENIC COMPOUNDS 



Laboratory Preparation 

In the laboratory, ethyl dichloroarsine may be obtained by 
the action of ethyl iodide on sodium arsenite by a method 
similar to that described already for the preparation of methyl 
dichloroarsine 1 : 

In a wide-mouthed vessel A (see Fig. 16) of about 2 litres 
capacity, fitted with a mercury-sealed mechanical stirrer B, and a 



condenser C, 50 gm. of arsenious oxide are dissolved in a sodium 
hydroxide solution containing 60 gm. NaOH and 500 ml. water. 
100 gm. ethyl iodide are added and the stirrer started. The vessel 
is then heated in a water-bath for 2 hours, the bath being 
gradually raised to boiling. 

The solution obtained is transferred to a distillation flask and 
heated in a brine bath. Ether, alcohol and excess ethyl iodide 
pass over, and then the residue is cooled and carefully neutralised 
with sulphuric acid (d. 1-84), 90 gm. methyl sulphate are added 
and the methyl iodide is distilled off on the water-bath. 2 After 

1 Nekrassov, loc. cii. 

2 As the formation of the ethyl arsenic acid and the succeeding chlorination 
of the ethyl arsenious oxide takes place in acid conditions, hydriodic acid, which is 
presentin considerable quantity, can form ethyl diiodoarsine. In order to prevent 
this happening, the iodine is removed as methyl iodide by addition of dimethyl 
sulphate, which reacts, as discovered by Wieland (Ber., 1905, 38, 2327), in the 
following manner : 





ft 



Fig. 16. 




ETHYL DICHLOROARSINE : MANUFACTURE 281 



adding 500 ml. concentrated hydrochloric acid (d. 1*19), the 
remaining liquid is quickly filtered through a pleated paper and a 
rapid current of sulphur dioxide is passed through the nitrate. 
The solution, which is at first coloured, becomes almost colourless 
and an oily layer is deposited at the bottom of the flask. This 
is separated in a tap-funnel, dried over calcium chloride and 
distilled in vacuo. Yield 75-80% of theoretical. 

Industrial Manufacture 

American Method. In America, a similar method was employed 
for the manufacture of ethyl dichloroarsine to that already 
described for methyl dichloroarsine. It consisted essentially in 
treating sodium arsenite with diethyl sulphate, then with diethyl 
sulphate, reducing the product obtained with sulphur dioxide 
and then chlorinating with hydrochloric acid. 

German Method. The method employed in Germany during the 
war of 1914-18 for the preparation of this substance differs from 
the American method only in the employment of ethyl chloride 
instead of diethyl sulphate. 

The principal stages in the manufacture are as follows : 

(1) Preparation of the sodium salt of ethyl arsenic acid : 

/ONa 

NaaAs0 3 + C 2 H 5 C1 = NaCl + C 2 H 6 -As^g N 

(2) Formation of ethyl arsenic acid : 

/ONa OH 
C^Asf O + 2 HCl = 2 NaCl + C,H 5 -As=0 
\ONa ^OH 

(3) Reduction to ethyl arsenious oxide : 
'OH 



/un 

C 2 H 5 -Asf O + S0 2 = C^AsO + H 2 S0 4 
\OH 



(4) Chlorination of the ethyl arsenious oxide : 

/CI 

C 2 H 5 AsO + 2 HCl = H 2 0 + C a H fi As^ ci 

Into an autoclave of 300 litres capacity a solution of sodium 
arsenite is first introduced. This is obtained by treating 100 parts 
of arsenious oxide with 300 parts of a 55% sodium hydroxide 
solution. The ethyl chloride is then added, in quantity 150 parts 
to each 100 parts of arsenious oxide, in three or four portions at 



282 



ARSENIC COMPOUNDS 



hourly intervals. The reaction between ethyl chloride and sodium 
arsenite, which lasts for some 10-12 hours, needs a temperature of 
90 0 to 95 0 C, and a pressure of 10-15 atmospheres. 

At the end of the reaction the ethyl alcohol formed from the 
ethyl chloride by hydrolysis is distilled off together with the 
excess of ethyl chloride, the residue being taken up again with 
water and transferred to a suitable vessel, where it is neutralised 
with sulphuric acid and reduced with sulphur dioxide while 
maintaining at 70° C. A heavy oil containing about 93% ethyl 
arsenious oxide is deposited. To convert this into ethyl 
dichloroarsine it is placed in a lead-lined iron vessel and completely 
saturated with gaseous hydrochloric acid, maintaining the internal 
temperature at 95° C. meanwhile. This operation needs about 
2 days. The product is distilled in vacuo until oily drops begin to 
come over. 

According to German claims, it is possible to obtain higher 
yields of ethyl dichloroarsine by this method than by the American 
method. 

Physical Properties 

Ethyl dichloroarsine is a mobile liquid with a characteristic 
odour which when highly diluted is reminiscent of fruit. It may 
be detected by this means at a concentration of 0-5 mgm. per cu. m. 
of air. It is colourless, becoming slightly yellow on exposure to 
air and light. It boils at ordinary pressure at 156 0 C. with 
decomposition, while at 50 mm. pressure it boils at 74 0 C. 1 and at 
11 mm. pressure distils unchanged at 43-5° C. Its melting point 
is - 65 0 C. 

The specific gravity of ethyl dichloroarsine at 14 0 C. is 1742, 
the coefficient of thermal expansion o-oon and the density of the 
vapour six times that of air. 

The volatility of ethyl dichloroarsine is lower than that of 
methyl dichloroarsine (Herbst) : 



The vapour pressure at 21-5° C. is 2-29 mm. of mercury. It 
is readily soluble in the organic solvents : alcohol, ether, benzene, 
acetone, cyclohexane. It also dissolves in water (1 gm. per 
1,000 ml. of water), hydrolysis taking place. 



TEMPERATURE 
°C. 

o 

20 



VOLATILITY 

mgm.jcu. m. 
6,510 



20,000 
27,200 



25 



1 Gibson and coll., /. Chem. Soc, 1931, 2518. 



ETHYL DICHLOROARSINE : PROPERTIES 283 



Chemical Properties 

The chemical behaviour of ethyl dichloroarsine is similar to 
that of methyl dichloroarsine. 

Water. Water hydrolyses dichloroarsine as follows : 

C 2 H 5 AsCl 2 + H 2 0 = C 2 H 6 AsO + 2HCI. 

The velocity of the hydrolysis is approximately equal to that 
of methyl dichloroarsine. The ethyl arsenious oxide which forms 
is a colourless oil, with a nauseating, garlic-like odour, but 
without vesicant action, which rapidly oxidises in the air to form 
colourless crystals. Its specific gravity is 1-802 at n° C, it boils 
at 158° C. at 10 mm. mercury pressure 1 and is soluble in benzene, 
ether and acetone. 

Nitric Acid. By prolonged heating of ethyl dichloroarsine 
with dilute nitric acid, acicular crystals of ethyl arsenic acid, 
melting at 95 0 to 96 0 C. (Dehn) 2 or 99 0 to ioo° C. (Backer) 3 and 
soluble in water and alcohol, are formed. 

Hydrogen Peroxide. Like nitric acid, hydrogen peroxide 
converts ethyl dichloroarsine into ethyl arsenic acid (Backer) : 

/OH 

CjHsAsCla + 2 H 2 0 2 = C^As^O^ + 2 HC1 + O 

Sodium Iodide. Ethyl dichloroarsine reacts with sodium 
iodide in acetone solution to form ethyl diiodoarsine 4 : 

C 2 H 5 AsCl 2 + 2NaI = C 2 H 5 AsI 2 + aNaCl. 

an oily, yellow liquid, boiling at 126° C. at 11 mm. pressure. On 
cooling with solid carbon dioxide a crystalline mass forms which 
melts at — 9 0 C. 

Hydrogen Sulphide. By the action of hydrogen sulphide in 
aqueous or alcoholic solution on ethyl dichloroarsine, ethyl 
arsenious sulphide separates 5 : 

C 2 H 8 AsCl 2 + H 2 S = C s H 6 AsS + 2HCI. 

This is a yellow oil which is soluble in chloroform and carbon 
disulphide and has a density of 1-8218 at 17 0 C. 8 

This reaction with hydrogen sulphide may be used for the 
detection of small quantities (0-02-0-05 mgm.) of ethyl 
dichloroarsine (see p. 328). 

1 W. Steinkopf and W. Mieg, Ber., 1920, 53, 1013. 

! Dehn and McGrath, /. Am. Chem. Soc, 1906, 28, 347. 

* Backer, Rec. trav. Chim., 1935, 54, 186. 

* Burrows and Turner, /. Chem. Soc, 1920, 117, 1373. 

6 S. Nametkin and W. Nekrassov, Z. anal. Chem., 1929, 77, 285. 

* Kretov and Berlin, /. Obscei Khim., Ser. A., 1931, 1» 4"- 



284 



ARSENIC COMPOUNDS 



Calcium Hypochlorite. Ethyl dichloroarsine is easily decomposed 
by calcium hypochlorite, either solid or in aqueous suspension. 1 
Because of this property, chloride of lime is employed for the 
decontamination of objects contaminated with ethyl dichloroarsine. 

Ethyl dichloroarsine, when dry, does not attack iron even at 
a temperature of 50° C. It corrodes brass strongly, however. 

During the war of 1914-18, it was employed both alone and 
mixed with other substances. The two mixtures most commonly 
employed were : 

(a) Dichloromethyl ether 18%, ethyl dichloroarsine 37%, ethyl 
dibromoarsine 45%. 

(b) Dichloromethyl ether 20%, ethyl dichloroarsine 80%. 
The minimum concentration capable of perceptible irritant 

action is 1-5 mgm. per cu. m. of air according to Lindemann. The 
maximum concentration supportable by a normal man for up 
to 1 minute is 5-10 mgm. per cu. m. (Lustig). The mortality- 
index is 3,000 according to Miiller ; according to Prentiss it is 
5,000 for 10 minutes' exposure and 3,000 for 30 minutes' exposure. 

This substance, like methyl dichloroarsine, has a vesicant 
action on the skin, 2 which, according to Strughold, 3 is perceptible 
at a concentration of 1 mgm. per sq. cm. of skin. 

3. The Chlorovinyl Arsines (Lewisite) 

The study of the action of acetylene on arsenic trichloride 
which, according to Lewis, was started in America in 1904 
(Griffin), was recommenced during the last war almost simul- 
taneously by German, 4 American 6 and English 6 chemists. 

These studies have shown that arsenic trichloride does not 
react with acetylene, even when heated to boiling, but mixed with 
aluminium chloride it absorbs a considerable quantity of acetylene 
with development of heat. In this reaction, a brown oil is formed 
which consists of a mixture of the following three compounds : 

/ CHCl-CHCl-AsCl 2 . CHCl-CHCl-AsCl, 

Alf CHCl-CHCl-AsCl 2 , Al/CHCl-CHCk 
\CHCl-CHCl-AsCl 2 \ )AsCl 

\CHC1-CHCK 
/ CHCl-CHCl \ 
Al<-CHCl-CHCl-4As 



1 Buscher, Giftgas ! Und Wir ? Hamburg, 1932. 

2 Hanzlik loc. cit. 

3 Strughold, Z. Biol., 1923, 78, 195. 

4 Defert, Monatsh., 1919, 40, 313 ; Wieland, Ann., 1923, 431, 30. 
6 Lewis and Perkins, Ind. Eng. Chem., 1923, 15, 290. 

6 Green, /. Chem. Soc, 1921, 119, 448; Mann and Pope, /. Chem. Soc , 
1922, 121, 1754. 



THE CHLOROVINYL ARSINES 285 

which are readily hydrolysed to give the following three 
substances : 

CI — CH=CH— AsCl 2 (CI — CH = CH) 2 AsCl (Cl-CH=CH) 3 As 

chloro vinyl dichloro vinyl trichloro vinyl 

dichloroarsine chloroarsine arsine 

In this mixture trichlorovinyl arsine always predominates and 
this substance has only a minor interest as a war gas, for its 
toxicity is low. Chlorovinyl dichloroarsine, which, besides its 
irritant action on the respiratory passages, also has a vesicant 
action similar to that of dichloroethyl sulphide, is of much 
greater importance. The resemblance in the properties of these 
two substances has been attributed to the presence of the two 
similar groups : 

CI — CHg — CHg — 
and CI— CH=CH— . 

Later, various other compounds were prepared and examined 
for possible employment as war gases. These are similar in 
constitution to the chlorovinyl arsines and are prepared similarly : 

ft Bromovinyl dibromoarsine (b.p. 140 0 to 143 0 C. at 16 mm. 
mercury pressure) was prepared by Lewis and Stiegler 1 by the 
action of acetylene on arsenic bromide mixed with aluminium 
chloride : 

/Br 

CH=CH + AsBr 3 = Br-CH=CH-As< 

x Br 

/? Chlorostyryl dichloroarsine (b.p. 108° to 110° C. at 12 mm.) 
was obtained by Hunt and Turner 2 by acting on arsenic 
trichloride with phenylacetylene : 

/CI 

C 6 H 5 -C=CH-As( 

/} Chlorovinyl methyl chloroarsine (b.p. 112° to 115° C. at 10 mm. 
mercury pressure) was obtained by Das Gupta, 8 by the action of 
acetylene on methyl dichloroarsine (see p. 278) in the presence of 
anhydrous aluminium chloride : 

/CI 
CH 3 -As< 

N CH=CH-C1 



1 Lewis and Stiegler, /. Am. Chem. Soc, 1925, 47, 2546. 
* A. Hunt and E. Turner, /. Chem. Soc, 1925, 127, 996. 
» Das Gupta, /. Ind. Chem. Soc, 1936, 13, 305. 



286 



ARSENIC COMPOUNDS 



Phenyl ft chlorovinyl chloroarsine (b.p. 140° to 150° C. at 10 mm. 
mercury pressure) was obtained by the reaction of acetylene with 
phenyl dichloroarsine in the presence of aluminium chloride : 



All these compounds, like the chlorovinyl arsines, are oily 
substances, somewhat yellow in colour, with extremely unpleasant 
odours. Their aggressive properties are still rather indefinite 
with the exception of ft chlorovinyl methyl chloroarsine, which 
does not irritate the nasal tissues like the chlorovinyl arsines, but 
produces blisters on the skin which heal only with difficulty. 

Several compounds obtained by the action of ethylene on 
arsenic trichloride have also been prepared. Such, for example, is 
ft chloroethyl dichloroarsine 1 : 



This is a liquid with a boiling point of 93 0 to 94° C. at a pressure 
of 16 mm. of mercury which is both irritant and vesicant in its 
action. In the liquid condition, it penetrates linen and rubber ; 
in the vapour state, at concentrations which can be obtained in 
practice, it has no action on the human skin. 2 

Preparation of the Chlorovinyl Arsines 

The mixture of the three chlorovinyl arsines is obtained, as 
indicated above, by the action of acetylene on arsenic trichloride. 

ft Chlorovinyl dichloroarsine may also be obtained by the 
reduction of a hot solution of ft chlorovinyl arsenic acid which 
has been acidified with hydrochloric acid, by means of sulphur 
dioxide, hydriodic acid being employed as a catalyst. 3 Another 
method of preparation is to heat a mixture of arsenic trichloride 
and trichlorovinyl arsine in a closed tube at 220° C. for 4 hours. 
The following reaction takes place 4 : 



Laboratory Preparation 

In the laboratory, the preparation of the chlorovinyl arsines 
may be carried out by condensing arsenic trichloride with 

1 Renshaw and Ware, /. Am. Chem. Soc, 1925, 47, 2991 ; Scherlin and 
Epstein, Ber., 1928, 61, 1821 ; Nekrassov, Ber., 1928, 61, 1816. 

2 Ferrarolo, Minerva Medica, 1935 (II), 37, 30. 

3 Gibson and Johnson, /. Chem. Soc., 1931, 753. 

* Green and Price, /. Chem. Soc., 1921, 119, 448. 



Cl-CH=CH-As< 





CI 



CI 



(ClCH=CH) 3 As + 2AsCl 3 — >- 3CICH = CHAsCl 2 . 



CHLOROVINYL ARSINES : PREPARATION 287 



acetylene in presence of aluminium chloride. The apparatus 
used is shown in Fig. 17. 45 gm. arsenic trichloride are placed in 
the vessel A, together with 15 gm. anhydrous aluminium chloride. 
While stirring and cooling with water, 6-8 litres of acetylene, 
which have been passed first through a sulphuric acid wash- 
bottle and then through a calcium chloride column C, are bubbled 
in. The reaction is accompanied by the evolution of heat, and 
the mixture should be cooled in order to maintain the temperature 
between 30° and 35 0 C. When the acetylene has been added, 
the reaction mixture is poured slowly into 200 ml. hydrochloric 




Fig. 17. 



acid cooled to about o° C. An oily layer forms and this is 
separated and fractionally distilled at reduced pressure (20-30 
mm.). The arsenic trichloride which has not reacted distils first 
and then the chlorovinyl arsines as follows : 

First fraction . 90° to 105° C. chlorovinyl dichloroarsine. 
Second fraction . 125° to 140° C. dichlorovinyl chloroarsine. 
Third fraction . 145° to 160 0 C. trichlorovinyl arsine. 

Preparation of Chlorovinyl Dichloroarsine and Dichlorovinyl 
Chloroarsine from Trichlorovinyl Arsine. 1 80 gm. trichlorovinyl 
arsine and 66-2 gm. arsenic trichloride are placed in a thick-walled 
glass tube which is then sealed in the flame. The tube is placed 
in an outer tube of steel, covered with asbestos, and the whole 
heated for 4 hours at 220° to 250 0 C. After allowing to cool, the 
glass tube is opened at the end and the oily contents distilled 
under reduced pressure. The products obtained are as follows : 

56 gm. chlorovinyl dichloroarsine. 
80 gm. dichlorovinyl chloroarsine. 

1 Green and Price, /. Chem. Soc, 1921, 119, 448. 



288 



ARSENIC COMPOUNDS 



Industrial Manufacture 

The process used in America for the manufacture of the 
chlorovinyl arsines may be summarised as follows 1 : 

6*3 kgm. arsenic trichloride and i-i6 kgm. aluminium chloride 
are placed in a 2-gallon enamelled autoclave, and while they are 
continually stirred, a current of acetylene which has been dried 
with sulphuric acid and calcium chloride is bubbled in. The 
quantity of acetylene used is measured by means of a rotary 
gas-meter ; it is in equimolecular amount with the arsenic 
trichloride. During this operation the temperature slowly rises 
from 25 0 to 30 0 C. initially to 40 0 to 45 0 C, but it should in any 
case be kept below 6o°C. When all the acetylene has been 
absorbed (about 2 hours) the product is separated by washing 
first with 20% hydrochloric acid, which extracts the arsenic 
chloride, and distilling the residue. This is carried out in a special 
cast-iron still of about 1 gallon capacity. The distillate is then 
fractionally distilled once more under reduced pressure to 
separate the three chlorovinyl arsines. 

Physical and Chemical Properties 

The three chlorovinyl arsines are colourless liquids at ordinary 
temperatures and, if pure, are stable. In presence of small 
quantities of arsenic trichloride, however, they become violet or 
brown in time, and the speed of this change as well as the final 
colour seems to depend on the quantity of arsenic chloride 
present. 

They have high boiling points (190° to 260 0 C), but on heating 
at ordinary pressure easily decompose. Chlorovinyl dichloroarsine 
is thus decomposed into dichlorovinyl chloroarsine and arsenic 
trichloride, dichlorovinyl chloroarsine into chlorovinyl dichloro- 
arsine and acetylene, etc. This behaviour supports the belief 
that an equilibrium exists between the three chlorovinyl arsines 
and their components, acetylene and arsenic trichloride. The 
hypothesis is confirmed by the observation that from the reaction 
between acetylene and arsenic trichloride, it is not possible to 
produce any one of these compounds solely ; a mixture of all 
three is always obtained. 

They are sparingly soluble in cold water or in dilute acids, but 
all — except trichlorovinyl arsine, which is insoluble in alcohol — 
dissolve readily in alcohol, benzene, kerosene, olive oil, petrol 
and other organic solvents. 

1 Detailed accounts of the best conditions for carrying out the reactions may 
be found in Ind. Eng. Chem., 1923, 15, 290. 



p CHLOROVINYL DICHLOROA RSINE 289 



Chemically, they are unsaturated and unstable compounds. 
As Conant 1 has pointed out, they all have a chlorine atom 
attached to that carbon of the vinyl group which is not adjacent to 
the arsenic atom. The following are therefore their correct names : 

/? chlorovinyl dichloroarsine. 
)8j8' dichlorovinyl chloroarsine. 
PP'fi" trichlorovinyl arsine. 

(a) p Chlorovinyl dichloroarsine (M.Wt. 207 3) 

XI 

CI— CH = CH— As< 

X C1 

Physical Properties 

Chlorovinyl dichloroarsine when pure is a colourless liquid 
which boils at ordinary pressures at 190° C, with decomposition. 
At reduced pressure, however, it distils unchanged at the 
following temperatures : 



MM. PRESSURE B.P. ° C. 

30 96-98 (Lewis and Perkins) 

24 93-94 (Burton and Gibson) 2 
15 79 (Lewis and Perkins) 

12 77-78 (Wieland) 
10 76 (Gibson and Johnson) 3 

10 72 (Lewis and Perkins) 



The melting point is -f o-i° C. according to Gibson and 
Johnson, — 13 0 C. according to Nekrassov, and — 18-2° C. 
according to Libermann. 

The odour of this substance recalls that of geraniums and is 
perceptible even at a dilution of 14 mgm. per cu. m. of air 
(Prentiss) . 

In the following table the specific gravity and corresponding 
specific volume are given at various temperatures : 



Temperature (° C.) 


S.G. 


Specific Volume 


O 


1-9200 


0-5232 


IO 


1-9027 


0-5255 


15 


1-8940 


0-5279 


20 


1-8855 


0-5302 


25 


1-8768 


0-5328 


30 


1-8682 


0-5352 


40 


I-85I3 


0-5401 


50 


I-8338 


Q-5453 


60 


1-8164 


0-5505 



1 Chemical Warfare Communications, Offense Research Section of the U.S. 
Chemical Warfare Service (see Ind. Eng. Chem., 1923, 15, 290). 

2 Burton and Gibson, /. Chem. Soc, 1926, 464. 
s Gibson and Johnson, /. Chem. Soc, 1931, 754. 



ARSENIC COMPOUNDS 



The vapour tension of /? chlorovinyl dichloroarsine at tempera- 
ture t may be calculated from the formula (see p. 5). 

, 2781.69 
log p = 9.123 -^fi 

In the following table are given the values of the vapour 
tension at various temperatures : 

Temperature Vapour Tension 

° C. MM. MERCURY 

o 0-087 

10 0-196 

20 0-394 

30 0-769 

40 1-467 

50 2-679 

75 9-66 

100 32-50 

150 175-0 

175 487-6 

Following are the values of the volatility of jS chlorovinyl 
dichloroarsine 1 : 

0 C. MGM. PER CU. M. 

O 1,000 

20 2,300 
40 15,600 

The latent heat of vaporisation is 57-9, the mean coefficient of 
thermal expansion between o° C. and 50 0 C. is 0-00094 and the 
vapour density is 7-2. 

It is readily soluble in benzene, absolute alcohol, olive oil, 
kerosene and other organic solvents. It is sparingly soluble in 
water (about 0-5 gm. in 1,000 ml.). 2 

Chemical Properties 

Owing to the unsaturated character of the molecule and the 
presence of two chlorine atoms attached to the arsenic atom, this 
substance is highly reactive. 

Water. In contact with water, or with a damp atmosphere, 3 
/? chlorovinyl dichloroarsine is rapidly decomposed even at 
ordinary temperatures, the following reaction taking place : 

/CI H\ 

Cl-CH=CH-As( + >0 = 2 HC1 + Cl-CH=CH-As-0 
X C1 W 

1 Shiver, /. Chem. Education, 1930, 7, 108 ; Vedder, The Medical Aspects of 
Chemical Warfare, Baltimore, 1925. 

a S. Nametkin and W. Nekrassov, Z. anal. Chem., 1929, 77, 285. 
* Lewis and Perkins, Ind. Eng. Chem., 1923, 15, 290. 



P CHLOROVINYL DICHLOROA RSINE 291 



The degree of hydrolysis is notably increased by an increase 
in the temperature. The chlorovinyl arsenious oxide formed is a 
white, crystalline powder, sparingly soluble in water, alcohol and 
carbon disulphide and melting at 143 0 C. This oxide is also 
formed on treating /? chlorovinyl dichloroarsine with aqueous 
ammonia solution : 

ClCH=CHAsCl 2 + NH 4 OH = ClCH=CHAsO + NH 4 C1 + HC1. 

Alkalies. Alkalies completely decompose the molecule. Green 
and Price 1 have shown that on adding even very dilute cold 
solutions of sodium hydroxide or carbonate, chlorovinyl arsenious 
oxide is never obtained, but acetylene and arsenious acid, as 
follows : 

/CI 

Cl-CH=CH-As^ ci + 6 NaOH = N^AsGv, + 3 NaCl + C 2 H 2 4- 3 H 8 0 

When a 15% sodium hydroxide solution is employed at 
temperatures below 37° C, this decomposition takes place 
quantitatively, and only in the case of £ chlorovinyl dichloroarsine. 
This fact may be used for the quantitative determination of 
£ chlorovinyl dichloroarsine in presence of dichlorovinyl chloro- 
arsine and trichlorovinyl arsine (Lewis) . 

Halogens. The halogens readily react with chlorovinyl 
dichloroarsine. Thus on adding a dilute solution of bromine in 
carbon tetrachloride to a solution of £ chlorovinyl dichloroarsine 
in the same solvent, the colour of the bromine gradually disappears 
while small lamellae of a bromo-derivative separate. This melts 
at 122° C, and its formation has been suggested by Green and 
Price as a means of detecting chlorovinyl dichloroarsine. 2 

Nitric Acid. Chlorovinyl dichloroarsine, when treated with 
nitric acid, is oxidised to £ chlorovinyl arsenic acid 3 

/OH 
Cl-CH=CH-As4=0 
\OH 

If concentrated nitric acid is employed, this oxidation is very 
violent and it is necessary to cool the reaction mixture. On the 
other hand, when dilute nitric acid is employed it is necessary 
to warm it in order to carry out the reaction. On standing, a 
colourless crystalline mass separates ; this is 0 chlorovinyl 
arsenic acid which may be purified by recrystallisation from a 

1 Green and Price, /. Chem. Soc, 1921, 119, 448. 
a Green and Price, loc cit. 

3 Mann and Pope, /. Chem. Soc, 1922, 121, 1754. 

10—2 



292 



ARSENIC COMPOUNDS 



mixture of acetone and carbon tetrachloride. It forms needles, 
melts at 130° C. and is soluble in water and alcohol. 

On warming this acid with a concentrated sodium hydroxide 
solution it is completely decomposed into acetylene, arsenic acid 
and hydrochloric acid : 



/OH 

Cl-CH=CH-AstO + 3 NaOH = Na 3 As0 4 + C 2 H 2 + HC1 + 2 H 2 0 
\OH 



When it is heated in vacuo to no 0 to 115 0 C, the acid loses a 
molecule of water and forms the corresponding anhydride : 

//° 

Cl-CH=CH-As{ 

^O 

This anhydride is a white hygroscopic powder which decomposes 
violently at 242° C. 

Hydrogen Peroxide. Chlorovinyl dichloroarsine reacts with 
hydrogen peroxide forming chlorovinyl arsenic acid, as with nitric 
acid 1 : 

Cl-CH=CH-AsCl 2 + 2 H 2 0 2 = 

/ OH 

= Cl-CH=CH-Asf O + 2 HC1 + O 
\OH 

Potassium Iodide. Potassium iodide reacts with jS chlorovinyl 
dichloroarsine with evolution of heat and formation of 
(3 chlorovinyl diiodoarsine : 



-As<! 



C1-CH=CH 

This iodo-derivative forms yellowish-brown crystals, m.p. 
37'5° to 3 8 '5° c - I1; is sparingly soluble in ligroin, but readily in 
alcohol and benzene. 2 

Hydrogen Sulphide. By the action of hydrogen sulphide on 
/? chlorovinyl dichloroarsine in alcohol solution, the corresponding 
sulphide, 3 C1CH = CHAsS, is formed. When pure, this forms a 
plastic mass insoluble in the usual organic solvents except carbon 
disulphide. It has a strong irritant action on the organism.* 
A method of detecting chlorovinyl dichloroarsine is based on the 
formation of this sulphide 5 (see p. 328). 

1 Wieland, Ann., 1923, 431, 38. 

1 W. Lewis and H. Stiegler, /. Am. Chem. Soc, 1925, 47, 2551. 
s Kretov and coll., /. Obscei Khim., Ser. A, 1931, 1, 411. 
* Lewis and Stiegler, loc. cit. 

' S. Nametkin and W. Nekrassov, Z. anal. Chem., 1929, 77, 285 



P? DICHLORO VINYL CHLOROARSINE 



Diphenylamine. Chlorovinyl dichloroarsine reacts on heating 
with diphenylamine to form 10 chloro 5-10 dihydro phenarsazine 1 : 

ClCH=CHAsCl 2 +(C 6 H 5 ) 2 NH = NHfCeH^AsCl+CH^CHCl+HCl 

in canary-yellow crystals with melting point 191° to 193° C. 
(see p. 323). Pure /? chlorovinyl dichloroarsine when kept in glass 
vessels is stable at ordinary temperatures, particularly in absence 
of light, while in presence of iron it is slowly converted into 
dichlorovinyl chloroarsine and trichlorovinyl arsine. 

It does not attack steel appreciably and when stored in 
projectiles causes only a slight superficial rusting of the metal 
walls. However, it attacks lead slightly and is itself partially 
decomposed. 

/? Chlorovinyl dichloroarsine has an irritant action on the eyes 
and on the respiratory tract. The minimum concentration 
causing irritation is o-8 mgm. per cu. m. of air ; that is to say, 
less than can be detected by odour (Prentiss). The fatal 
concentration, according to Vedder, is 48 mgm. per cu. m. for 
30 minutes' respiration. It also has a considerable vesicant action 
when allowed to remain in contact with the skin for a time. 8 

The lethal index is 1,500 according to M tiller, and 1,200 for 
10 minutes' exposure according to Prentiss. 

(b) jSjS' Dichlorovinyl Chloroarsine (M.Wt. 233 3) 

CI— CH=CH V 

>As— CI 
CI— CH=CH/ 

Physical Properties 

When pure, $9' dichlorovinyl chloroarsine is a clear transparent 
liquid of a yellow or yellowish-brown colour. It boils at ordinary 
pressure at 230° C. with decomposition. The boiling points at 
reduced pressures are as follows 3 : 

MM. MERCURY ° C. 

II 113 

15 119 
30 136 

The specific gravity at 20° C. is 1-702, and the vapour density 
8-1. 

1 Miller and coll., /. Am. Chem. Soc, 1930, 52, 4164; Gibson, /. Am. 
Chem. Soc, 1931, 53, 376. 

! H. Buscher, Grim- und Gelb-kreuz, Hamburg, 1932, 150. 

3 Lewis and Perkins, loc cit. ; Wieland, loc cit. ; Gryszkiewicz and coll., 
Bull. soc. chim., 1927, 41, 1750. 



294 ARSENIC COMPOUNDS 

The vapour tension of /?/?' dichlorovinyl chloroarsine may be 
calculated at any temperature t from the formula (see p. 5). 

3295-3 

log p = 9.983 — 



273 + t 



This substance is insoluble in dilute acids, but dissolves readily 
in alcohol and the common organic solvents. 



Chemical Properties 

Like the preceding compound, this also shows great chemical 
reactivity owing to the unsaturated character of the molecule : 

Water. Water hydrolyses it even at ordinary temperatures 
(Lewis and Perkins), the corresponding oxide being formed : 

2(C1CH = CH) 2 AsCl + H 2 0 = (C1CH = CHJjAs.O + 2HCI. 

This forms crystals melting at 62 0 to 63 0 C, insoluble in water, 
sparingly soluble in cold alcohol, but soluble in hot alcohol, and 
in ether. 

Alkalies. The alkalies decompose dichlorovinyl chloroarsine 
completely, forming acetylene and arsenious acid. This reaction, 
unlike the corresponding one with chlorovinyl dichloroarsine, 
takes place only above 37 0 C. and is never quantitative. 1 

Nitric Acid. By the action of concentrated nitric acid on 
/?/?' dichlorovinyl chloroarsine a crystalline product is obtained 
which melts at 97° to 99° C. ; this is the nitrate of /?/?' dichlorovinyl 
arsenic acid 2 : (ClCH=CH) 2 AsOOH.HN0 3 . This compound 
apparently does not ionise in solution, but when dissolved in 
aqueous alcohol and treated with sodium hydroxide solution 
until the nitric acid is neutralised, decomposition takes place. 
On extracting with chloroform and evaporating the extract, a 
crystalline mass remains which consists of dichlorovinyl arsenic 
acid (Mann and Pope), (CHCl=CH) 2 AsOOH. This is purified by 
recrystallisation from water or carbon tetrachloride, when it 
melts at 120 0 to 122° C. Like cacodylic acid, it is amphoteric, 
forming salts with acids as well as with bases. 

According to Green and Price this reaction with nitric acid 
may be employed very conveniently for the identification of 
dichlorovinyl chloroarsine. 

Hydrogen Peroxide. This arsine also is vigorously oxidised by 
hydrogen peroxide (Wieland). After evaporating the solution, 
dichlorovinyl chloroarsine remains as an oil which solidifies after 



1 Lewis and Perkins, loc. cit. 

2 Mann and Pope, loc. cit. 



j6P'/S" TRICHLORO VIN YL ARSINE 



295 



a time. It crystallises from hot water in brilliant prisms which 
melt at 120 0 to 122 0 C. 

Potassium Cyanide. When an alcoholic solution of j8/3' dichloro- 
vinyl arsine is treated with potassium cyanide, it is converted 
into )8j8' dichlorovinyl cyanoarsine, 1 (ClCH=CH) 2 AsCN, which 
is a colourless oil with a high toxicity (Libermann). 

Hydrogen Sulphide. When hydrogen sulphide is passed into a 
solution of dichlorovinyl chloroarsine in absolute alcohol an 
exothermic reaction takes place and dichlorovinyl arsenious 
sulphide is formed : 

(C1CH = CH) 2 As— S— As(CH = CHC1) 2 . 

This is a viscous, yellowish-brown substance, soluble in alcohol, 
insoluble in water, having vigorous irritant properties on the 
mucous membranes and a nauseating odour (Lewis). 

Chloramine-T. Treatment of dichlorovinyl chloroarsine with 
an equivalent amount of chloramine-T (CH 3 = C 6 H 4 — SO 2 Na = NCI) 
produces no additive-compound, unlike trichlorovinyl arsine. 

The biological action of dichlorovinyl chloroarsine is similar to 
that of chlorovinyl dichloroarsine, but less violent. 

(c) #S'jS" Trichlorovinyl arsine (M.Wt. 259-4) 

(C1CH = CHJsAs. 

Physical Properties 

$9'£" Trichlorovinyl arsine boils at atmospheric pressure at 
260° C. with decomposition, but distils unaltered at 138° C. at 
12 mm. pressure. On cooling, it solidifies in large crystals with 
m.p. 21-5° C. 2 It has a specific gravity at 1-572 at 20 0 C. and has 
a vapour density of 9. 

The vapour tension at temperature t may be calculated from 
the following formula (see p. 5). 

3312.4 

log p = 9-159 — 

' 273 + t 

It is not miscible with water or with dilute acids, but dissolves 
readily in the common organic solvents except alcohol. It differs 
in this respect from the other two chlorovinyl arsines which are 
both soluble in all proportions in alcohol. This, and its melting 
point, may be used for its detection. 

1 Lewis and Stiegler, /. Am. Chem. Soc, 1925. 47, 2553. 

2 Various values for the melting point of this substance are quoted in the 
literature : 3° to 4 0 C. (Green and Price) ; 13 0 C. (Wieland) ; 23 0 C (Pope). 



296 



ARSENIC COMPOUNDS 



Chemical Properties 

Water. Trichlorovinyl arsine does not react with water and 
may be distilled in steam without any decomposition. 

Halogens. On adding a solution of bromine in benzene to a 
benzene solution of trichlorovinyl arsine, cooled in a freezing 
mixture, small colourless needles separate, melting at 107 0 C. 
They consist of trichlorovinyl dibromo arsine (Mann and Pope) : 

/Br 

(Cl-CH=CH) 3 As<^ 

On treating this dibromo compound with hydrogen sulphide, 
it decomposes to form hydrobromic acid and trichlorovinyl 
arsine and deposit sulphur : 

/Br H\ 

(Cl-CH=CH) 3 As( + >S = (Cl-CH=CH) 3 As + S + 2 HBr 
N Br H' 

Nitric Acid. Concentrated nitric acid reacts vigorously with 
trichlorovinyl arsine, and in order to moderate the violence of the 
reaction, it is advisable to treat a small quantity of trichlorovinyl 
arsine (not more than 2 gm.) with an equal volume of nitric acid 
and warm cautiously. On allowing to cool, a colourless crystalline 
mass is deposited and when this is crystallised from chloroform, 
small needles, melting at 103° C. are obtained. This substance 
is trichlorovinyl hydroxyarsonium nitrate. 

/OH 
(Cl-CH=CH) 3 As( 

N N0 3 

When this nitrate is treated with an aqueous solution of sodium 
hydroxide in equivalent quantity, the product extracted with 
chloroform and the solvent evaporated, a crystalline residue 
remains. This consists of trichlorovinyl arsenic oxide 
(C1CH = CH) 3 AsO. On crystallising this from benzene containing 
a little chloroform, long colourless needles are obtained melting 
at 154° C. with decomposition (Mann and Pope). 

Chloramine-T. This tertiary arsine condenses with chloramine-T 
(CH 3 — C 6 H 4 — S0 2 Na : NCI) to give an additive compound of the 
formula (C1CH = CH) 3 As = N — S0 2 — C 6 H 4 — CH 3 . This contains 
the grouping 

: As = N— 

which according to Mann and Pope may be termed the 
" arsilimine " group, by analogy with the sulphilimine group 

: S = N— 



THE AROMATIC ARSINES 



297 



This compound may be obtained by treating an acetone 
solution of the tertiary amine (1 molecule) with chloramine-T 
(1 molecule) and boiling for 20 minutes. The product is filtered, 
the nitrate evaporated to dryness and the residue crystallised 
several times from ether. Colourless plates, melting at 124 0 C. 

Unlike the previous two compounds, trichlorovinyl arsine has 
no irritant action on the skin or the respiratory organs. 

(B) AROMATIC ARSINES 

The aromatic arsines were first employed as war gases in July, 
1917, by the Germans, and their use undoubtedly marked a 
considerable step in the progress of the chemical arm. 

These arsines differ from those of the aliphatic series which have 
just been described, by their physical and chemical properties, 
and by their method of employment, as well as by their biological 
action. They are solids or liquids with high boiling points, have 
very low vapour tensions, are quite resistant to heating and are 
only oxidised by atmospheric oxygen with difficulty. 

In order to obtain them sub-divided in the air they are employed 
dissolved in other war gases, or are filled into special containers 
so that they surround the bursting charge, or else are mixed with 
substances whose temperature of combustion is sufficiently high 
to cause the arsines to form a cloud (candles, generators, etc.). 
By these means disperse systems (aerosols) are formed in which 
the dispersed phase consists of extremely minute particles of the 
arsine. These remain suspended in the air for a considerable time 
and are not filtered out by activated carbon. 

Physiologically, these compounds have a lower toxicity than 
the aliphatic arsines. However, they act as energetic sternutators 
and irritants, even at very low concentrations. This action is 
produced immediately after 1-2 minutes' exposure to concentra- 
tions of o-2-o*5 mgm. substance per cu. m. of air. 

During the war much diphenyl chloroarsine was employed. 
However, in May, 1918, it was largely substituted by diphenyl 
cyanoarsine by the Germans because of the superior physio- 
pathological effects of the latter. Diphenyl cyanoarsine is 
considered as the most irritant substance employed during the 
war. 

Since the war several other substances similar to diphenyl 
chloroarsine have been the subjects of experiments. For instance, 

Diphenyl chlorostibine, white crystals melting at 68° C., 1 and 
diphenyl cyanostibine, crystals melting at 115° to 116° C. 2 The 

1 Michaelis and Guenter, Ber., 1911, 44, 2316. 
a W. Stejnkopf and coll., Ber., 193 2 . 65. 4°9- 



298 ARSENIC COMPOUNDS 

biological action of these substances is similar to that of the 
aromatic arsines described in this chapter. 1 

Recently several arsenical derivatives of naphthalene have 
been prepared : 

Naphthyl methyl chloroarsine : 

CloH;\ 

)AsCl 

ch/ 

and Naphthyl methyl fluoroarsine : 

)AsF 



CH 3 

The biological properties of these have not been reported in 
the literature. 2 

1. Phenyl Dichloroarsine (M.Wt. 223) 

CI 

C 6 H 5 -As< 

\C1 

Phenyl dichloroarsine was prepared in 1878 by La Coste and 
Michaelis 8 by passing the vapours of benzene and arsenic 
trichloride through a heated tube. The product obtained was 
impure with the diphenyl compound and could be purified by 
distillation or crystallisation only with some difficulty. The same 
workers later studied another method for its preparation. 4 This 
is more convenient and consists in heating mercury diphenyl to 
250° C. with an excess of arsenic trichloride. 

Phenyl dichloroarsine may also be obtained by heating 
triphenylarsine with arsenic trichloride in a closed tube to 250° C. 
for 30 hours 5 : 

As(C 6 H s ) 3 + 2AsCl 3 = 3 C 6 H 5 AsClj, 

or by heating phenyl mercuri-chloride with arsenic trichloride to 
100° C. for 4-5 hours (Roeder and Blasi's method). 6 

Laboratory Preparation 

Roeder and Blasi's method, mentioned above, is usually 
employed for the preparation. 50 gm. mercuric acetate are 
dissolved in 50 ml. acetic acid in a thick-walled flask. 100 ml. 
benzene, free from thiophene, are added and the mixture heated 

1 Flury, Z, ges. expt. Med., 1921, 13, 566. 

2 Sporzynsky, Roczniki Chem., 1934, 14, 1293. 

3 La Coste and Michaelis, Ber., 1878, 11, 1883. 

4 La Coste and Michaelis, Ann., 1880, 201, 196. 

• Michaelis and Reese, Ber., 1882, 15, 2876. 

• Roeper and Blasi, Ber., 1914, 47, 2751. 



PHENYL DICHLOROARSINE : PROPERTIES 299 



for 5 hours in a boiling water-bath. After cooling, the insoluble 
part is filtered off and washed well with benzene, and the filtrate 
is evaporated to a small volume. Phenyl mercuri-chloride is 
thus obtained. 30 gm. of this are weighed into a flask, 100 gm. 
arsenic trichloride added and heated on the water-bath to ioo° C. 
for 4-5 hours. A viscous suspension is formed first and then 
this is suddenly converted into a brown liquid, while crystals 
separate below. After filtration, the filtrate is distilled under 
reduced pressure. The excess of arsenic chloride passes over 
first and then, at a much higher temperature, the phenyl 
dichloroarsine. 

Physical Properties 

Phenyl dichloroarsine when pure is a colourless liquid which 
gradually turns yellow. At ordinary pressures it boils at 255 0 to 
257° C. and at 14 mm. pressure at 124° C. At — 20 0 C. it 
solidifies to a microcrystalline mass. The specific gravity is 
1-654 at 2 °° c. 

Its vapour tension at temperature t may be calculated from 
the formula : 



The vapour tension at 15 0 C. is 0-014 mm. and the volatility at 
20 0 C. is 404 mgm. per cu. m. The coefficient of thermal expansion 
is 0-00073. 

It is insoluble in water, but easily soluble in the common 
organic solvents. 

Chemical Properties 

Water. Phenyl dichloroarsine on treatment with water is 
hydrolysed to phenyl arsenious oxide : 



This forms crystals melting at 142 0 C. 1 and is insoluble in water 
and ether but soluble in alcohol, benzene and chloroform. A 
polymer of phenyl arsenious oxide is also formed, probably a 
dirtier, of the formula 2 



3164 



log p = 9.150 — 



273 + t 



CgHsAsCLj + H 2 0 = 2HCI + C 6 H 6 AsO. 




which forms crystals melting at 2io° to 220 0 C. 



1 Blicke, /. Am. Chem. Soc, 1930, 52, 2946. 

2 Steinkopf and coll., /. prakt. Chem., 1934, Ml, 3°i- 



3ot> 



ARSENIC COMPOUNDS 



Alkali Hydroxides. Phenyl dichloroarsine is also hydrolysed 
by the action of alkali hydroxide solutions. The phenyl arsenious 
oxide in presence of excess alkali is converted to the salt of the 
corresponding phenyl arsenious acid : 

/ONa 

C 6 H 5 AsO + 2 NaOH = C 6 H s As( + H 2 0 

ONa 

Halogens. With chlorine and phenyl dichloroarsine, an additive 
compound is formed, tetrachloro phenylarsine. This decomposes 
into phenyl arsenic acid in the presence of moisture. 

Bromine, however, forms no additive compound. By treatment 
of phenyl dichloroarsine with excess of bromine, the molecule is 
decomposed with formation of dibromobenzene, arsenic chloro- 
bromide and hydrobromic acid, 1 as follows : 

C 6 H 5 AsCl 2 + 2Br 2 = C 6 H 4 Br 2 + AsBrCl 2 + HBr. 

Ammonia. By the action of gaseous bromine on phenyl 
dichloroarsine in benzene solution, phenyl arsenimide 2 is obtained: 

C„H 8 AsCl 2 + 3NH3 = C 6 H 6 AsNH + 2 NH 4 C1. 

This forms crystals melting at 26-5° C. and decomposes rapidly 
with formation of phenyl arsenious oxide by the action of water 
or even on exposure to moist air : 

C 6 H 6 AsNH + H 2 0 = C 6 H 6 AsO + NH 3 . 

Phenyl arsenimide both dispersed in the air and in solution 
has a very irritant action on the skin. 3 

Amines. Primary and secondary amines, both of the aliphatic 
and aromatic series, react vigorously with phenyl dichloroarsine, 
giving compounds of the following types : 

/NH-R /N(R) 2 
C 6 H 5 As( and C 6 H 5 As( 

N C1 X C1 

and liberating hydrochloric acid. With aniline, for example, a 
compound of the following structure is formed : 

/NHC 6 H 8 
C 6 H 6 As( 
N C1 

This is readily hydrolysed by the action of moisture forming 
phenyl arsenious oxide and aniline hydrochloride. 

1 Raiziss and Gavron, Organic Arsenical Compounds, New York, 1923, 115. 

2 MiCHAELis, Ann., 1902, 320, 291. 

8 Ipatiev and coll., Ber., 1929, 62, 598. 



PHENYL DICHLOROARSINE : PROPERTIES 301 



With diphenylamine, 10 chloro 5-10 dihydro phenarsazine is 
formed 1 : 

C 6 H 5 AsCl 2 + NH(C 6 H 5 ) 2 = Nh( * 4 )asC1 + C 6 H 6 + HC1 

C 6 H 4 

With tertiary aliphatic amines, additive products are formed ; 
triethylamine, for instance, forms : 



Hydrogen Sulphide. By the action of hydrogen sulphide on 
phenyl dichloroarsine in alcoholic solution, phenyl arsenious 
sulphide, 2 C e H 6 AsS, is produced in crystals melting at I52°C., 2 
or 174 0 to 176 0 C. 3 This reaction is very sensitive, and as the 
sulphide obtained is insoluble in water, its formation may be 
employed to detect small quantities of the arsine (0-05 mgm. in 
1 ml. water) . 

Silver Cyanide. By prolonged boiling (5 hours) of silver 
cyanide with phenyl dichloroarsine in benzene solution, phenyl 
dicyanoarsine, 4 C 6 H s As(CN) 2 , is formed as crystals with an 
odour which is both aromatic and also resembles hydrocyanic 
acid. It melts at 78-5° to 79-5° C, and is readily decomposed by 
water or even by damp air, with formation of phenyl arsenious 
oxide and hydrocyanic acid. 

Acid Chlorides. Phenyl dichloroarsine, when treated with 
the aliphatic acid chlorides, e.g., acetyl chloride, in carbon 
disulphide solution and in presence of aluminium chloride, forms 
acetophenone and arsenic trichloride 5 : 

C 6 H 5 AsCl 2 + CH3COCI = C 6 H 5 COCH 3 + AsCl 3 . 

With chloroacetyl chloride, chloroacetophenone is obtained 6 : 

C 6 H 5 AsCl 2 + CICH3COCI = C 6 H 5 C0CH 2 C1 + AsCl 3 . 

Dimethyl Arsine. With dimethyl arsine a white crystalline 
product, C 6 H 6 AsCl 2 . (CH 3 ) 2 AsH, is formed, which is readily 
decomposed by the action of moisture. 7 

1 Burton and Gibson, /. Chem. Soc, 1926, 464 ; Gibson, /. Am. Chem. Soc, 
1931. 53, 376. 

8 Kretov, /. Obscei Khim., Ser. A, 1931, 1, 411. 

8 Blicke, /. Am. Chem. Soc, 1930, 52, 2946. 

* Gryskiewicz and coll., Bull. soc. chim., 1927. 41, 1323. 
s Malinovsky, /. Obscei Khim., Ser. A, 1935, 5, 1355- 

9 Gibson and coll., Rec. trav. Chim., 1930, 49, 1006. 
' Dehn, /. Am. Chem. Soc, 1908, 40, 121. 




302 



ARSENIC COMPOUNDS 



Diphenyl Arsine. By the action of diphenyl arsine on phenyl 
dichloroarsine, arsenobenzene and diphenyl chloroarsine are 
formed 1 ; 



Pure phenyl dichloroarsine does not attack iron. 

Phenyl dichloroarsine was employed during the war of 1914-18 
first by the Germans as a solvent for diphenyl cyanoarsine and 
later by the French in admixture with 40% of diphenyl chloro- 
arsine under the name of " Stemite." 

Phenyl dichloroarsine is a lung irritant, a vesicant 2 and a 
lachrymatory. The maximum concentration which a normal 
man can support for not more than a minute is 16 mgm. per cu. m. 
of air (Flury). The mortality-product is 2,600 for 10 minutes' 
exposure (Prentiss). 

2. Diphenyl Chloroarsine (M.Wt. 264 5) 



Diphenyl chloroarsine was prepared in 1880 by La Coste and 
Michaelis 3 by heating mercury diphenyl with phenyl dichloroarsine : 



2C 6 H 5 -As( + (C 6 H 5 ) 2 Hg = 2 (C 6 H 8 ),As-Cl + HgCl 2 



Its employment in September 1917 was a great surprise to the 
Allies because of its peculiar physical properties which enabled 
it, when properly dispersed in the atmosphere, to pass through 
the respirator-filters then in use. 

Preparation 

Diphenyl chloroarsine may be prepared in various ways : 

(1) By heating arsenic trichloride with benzene in presence 
of aluminium chloride : 

2C 6 H 6 + AsCl 3 = (C 6 H 5 ) 2 AsCl + 2HCI. 

(2) By the decomposition of dichlorotriphenyl arsine, obtained 
by the action of chlorine on triphenyl arsine : 



4 C 6 H 5 AsCl 2 + 4 (C 6 H 5 ) 2 AsH = 

= 2 C 6 H 5 -As=As 



;-C 6 H 5 + 4 (CeH^sCl + 4 HC1 




(CeH s ) 3 As( (C 6 H 8 ) 2 AsCl + C 6 H S C1 



1 Blicke and Power, /. Am. Chem. Soc, 1932, 54, 3353. 

* Hanzlich, loc. cit. 

* Michaelis and La Coste, Ann., 1880, 201, 219. 



DIPHENYL CHLOROARSINE : PREPARATION 303 



(3) By the action of phenyl magnesium bromide on arsenious 
oxide. Triphenyl arsine is obtained at the same time. 1 

(4) By the reaction between phenyl dichloroarsine and diphenyl 
arsine 2 : 

4 C„H 5 AsCl 2 + 4 (C 6 H 5 ) 2 AsH 4 (C.HJ.AsCl +■ 

2 C 6 H 5 As=AsC 6 H B + 4 HC1 

(5) By the action of arsenic trichloride on lead tetraphenyl in 
toluene solution 3 : 

AsCl 3 + (C 6 H 6 ) 4 Pb = (C.H.J.AsCl + (C 6 H 6 ) 2 PbCl 2 . 

During the war the Allies, in order to obtain rapid production 
of diphenyl chloroarsine, followed the method of Michaelis, 4 
modified by Morgan and Vining. 5 This method consists in 
preparing triphenyl arsine from chlorobenzene and arsenic 
trichloride, in the presence of metallic sodium : 

3 C 6 H 6 C1 + AsCl 3 + 6Na = (C 6 H 6 ) 3 As + 6NaCl, 

and then heating this substance with more arsenic trichloride : 

2(C 6 H 5 ) 3 As + AsCl 3 = 3 (C 6 H 6 ) 2 AsCl. 

The Germans, however, used an entirely different process (see 
p. 306), based on the reaction between the diazonium salts and 
sodium arsenite which Bart had studied for the first time in 
1912. 6 

Laboratory Preparation 

The preparation of diphenyl chloroarsine in the laboratory 7 is 
most conveniently carried out by Pope and Turner's 8 modification 
of the method of Michaelis. 

57 gm. sodium cut into slices are placed in a round-bottomed 
flask fitted with a reflux condenser and covered with 300 ml. 
benzene containing 1-2% ethyl acetate (which catalyses the 
reaction). After allowing this mixture to stand for J hour (in 
order to activate the metal) 136 gm. chlorobenzene and 85% 
arsenic chloride are slowly added. After a few minutes the 
reaction is considerably accelerated, and if necessary the flask 
should be cooled externally with a freezing mixture. It is then 

1 Blicke and Smith, /. Am. Chem. Soc, 1929, 51, 1558. 

• Blicke and Power, /. Am. Chem. Soc, 1932, 54, 3353. 

• Goddard and coll., /. Chem. Soc, 1922, 121, 978. 

• Michaelis and Reese, Ber., 1882, 15, 2876. 

4 Morgan and Vining, /. Chem. Soc, 1920, 117, 780. 
« Bart, D.R.P. 250,264 ; Schmidt, Ann., 1920, 421, 159. 
7 Nenitzescu, Antigaz, 1929. No. 2. 
s Pope and Turner, /. Chem. Soc, 1920, 117, 1447. 



3°4 



ARSENIC COMPOUNDS 



allowed to remain in the freezing mixture for 12 hours, being 
agitated during the first 2 hours. The contents are then filtered, 
the precipitate washed with hot benzene and the combined 
wash-liquid and nitrate distilled until the thermometer reaches 
200° C. A yellow oil remains, consisting of triphenyl arsine, 
and, on cooling, this solidifies. 

30 gm. of the triphenyl arsine obtained are weighed into a 
wide-mouthed vessel and heated to 350 0 to 360 0 C. while 25-5 ml. 
arsenic trichloride are introduced drop by drop from a tap-funnel 
with a capillary outlet. A dark brown product is formed and on 
distilling this under reduced pressure, diphenyl chlororarsine is 
obtained. 

Industrial Manufacture 

The Allied Method. The manufacture of diphenyl chlor oar sine 
by the Allies, as indicated above, consisted of two main stages : 

(a) The preparation of triphenyl arsine. 

(b) The conversion of the triphenyl arsine into diphenyl 
chloroarsine. 

(a) Preparation of Triphenyl Arsine. An attempt was at first 
made to use Michaelis's method for the industrial manufacture of 
triphenyl arsine, that is, the reaction of sodium with a mixture of 
arsenic trichloride and chlorobenzene to which a little ethyl 
acetate had been added to accelerate the reaction 1 : 

3C 6 H 5 C1 + AsCl 3 + 6Na = (C 6 H 6 ) 3 As + 6NaCl. 

Various difficulties were encountered in the industrial applica- 
tion of this method, but these were in great part resolved by the 
modifications suggested first by Morgan and Vining and then by 
Pope and Turner. 

The apparatus employed by Pope and Turner for the prepara- 
tion of triphenyl arsine consists essentially of an iron reaction 
cylinder closed by an iron cover in which are fitted a thermometer, 
a mechanical agitator, a funnel, a condenser and a pipe connected 
with a vessel containing the sodium, which is covered with xylene. 

In order to prepare triphenyl arsine, the arsenic trichloride, 
the chlorobenzene and the xylene are first mixed in a separate 
vessel, and of this mixture a half is introduced into the reaction 
chamber after diluting with more xylene. 

The sodium container is heated to 110° C. and the reaction 
vessel is also warmed until it reaches about 70° C, when the 
fused sodium is added in small portions with constant stirring. 



1 Philips, Ber., 1886, 19, 1031. 



DIPHENYL CHLOROARSINE : MANUFACTURE 305 



After about 15 minutes the other half of the arsenic trichloride, 
chlorobenzene and xylene mixture is added. 

When all the sodium has been introduced, the agitation is 
continued until the temperature of the liquid tends to drop. At 
60° C. it is filtered through a press, the filtrate being collected in a 
still where it is heated to 220° C. in order to remove the solvent 
and unreacted chlorobenzene. A liquid remains which on cooling 
solidifies to a bright yellow, crystalline solid consisting of triphenyl 
arsine. 

By this method large quantities of triphenyl arsine may be 
prepared in a relatively pure condition and in a short time. But 
on the other hand it is somewhat inconvenient to have to work 
with molten sodium, which tends to solidify in the funnel through 
which it is introduced. 

These inconveniences may be eliminated to a great extent by 
using Pope and Turner's modifications. The apparatus employed 
by these workers consists of a vessel fitted with a reflux condenser. 
The sodium, freed from grease, is placed in the same vessel to 
which is then added the arsenic trichloride and the chlorobenzene. 
Benzene is employed as the solvent instead of xylene ; as this 
boils at 80° C. it maintains the temperature constant at the most 
favourable point for the reaction. 

By this method the reaction takes longer than by Morgan's 
method, but, on the other hand, it is easier to operate and gives a 
better yield of triphenyl arsine. 

(6) Conversion of Triphenyl Arsine into Diphenyl Chloroarsine. 
This conversion was carried out first by Michaelis and Weber by 
heating the triphenyl arsine with the calculated quantity of 
arsenic trichloride in a closed tube for 10 hours at 250° C. These 
workers showed that the conversion takes place in three distinct 
stages : 



b) 2 (C 6 H 5 ) 3 As + AsCl 3 = 3 (C 6 H 5 ) 2 AsCl 

c) (C 6 H 5 ) 3 As + C 6 H 5 AsCl 2 = 2 (C 6 H 5 ) 2 AsCl 

which arrive at a stage of equilibrium. Morgan and Vining 
studied the reaction in order to find the optimum conditions for 
obtaining the highest yield of diphenyl chloroarsine. They 
proposed heating the mixture of triphenyl arsine and arsenic 
trichloride in a rotating autoclave at 250° to 280° C, with an 
internal pressure rising to 4*2-7 kgm. per sq. cm. (60-100 lb. 
per sq. in.). After 2 hours the heating is stopped and the product 




'3 




'CI 



306 



ARSENIC COMPOUNDS 



distilled in a current of carbon dioxide at 20-30 mm. pressure. 
The following fractions are collected : 

First fraction, 150° to 190° C, consists of a mixture of phenyl 
dichloroarsine and diphenyl chloroarsine. 

Second fraction, 190 0 to 220° C, consists of diphenyl chloro- 
arsine. 

Third fraction, 220° to 250° C, consists of triphenyl arsine and 
diphenyl chloroarsine. 

The residue consists chiefly of triphenyl arsine, which is 
extracted with chloroform and treated, after evaporating off the 
solvent, with phenyl dichloroarsine in an autoclave. About 60% 
of diphenyl chloroarsine is thus obtained. 

Pope and Turner have also determined the optimum conditions 
for carrying out this reaction. They recommend heating the 
triphenyl arsine in an open vessel to 350 0 C. and then allowing the 
arsenic chloride to enter from a tap-funnel terminating in a 
capillary tube. 

The yield of diphenyl chloroarsine by this method, which has 
the advantage of being carried out at ordinary pressure instead of 
in an autoclave, as is necessary in Morgan's method, depends 
predominantly on the time employed in adding the arsenic 
trichloride. 

The English and French, employing the method of Michaelis, 
modified by Pope and Turner, succeeded in obtaining a 
mixture containing 60-65% diphenyl chloroarsine and 35-40% 
phenyl dichloroarsine, which was employed without further 
treatment. 

German Method. The several steps in the manufacture by this 
method may be expressed as follows, according to Norris 1 : 

(i) Preparation of diazobenzene chloride from aniline and 
nitrous acid : 

C 6 H 5 NH 2 + HN0 2 = 2 H 2 0 + C„H 6 N = NCI. 

(ii) Reaction of diazobenzene chloride with sodium arsenite : 

/ONa 

C 6 H 5 -N=N-C1 + Na3As0 3 = C^As^O^ + NaCl + N 2 

and formation of phenyl arsenic acid : 

/ONa /OH 
C 6 H s -AsfO + 2 HC1 = C 6 H 5 As40 + 2 NaCl 
\ONa \OH 



1 Norris, /. Ind, Eng. Chem., 1919, 11, 817. 



3o8 



ARSENIC COMPOUNDS 



the calculated quantity of sodium nitrite. When the diazobenzene 
hydrochloride has been prepared, a solution of sodium arsenite is 
slowly run in. This latter is prepared beforehand by dissolving 
arsenious oxide in an aqueous sodium hydroxide solution which 
contains sufficient alkali to neutralise all the acid in the diazo 
solution and sufficient arsenious oxide to be 20% in excess of the 
theoretical quantity. 20 kgm. copper sulphate are also added to 
the diazotisation to accelerate the reaction. 

The mixture is stirred continuously and maintained for 3 hours 
at 15 0 C, when sodium phenyl arsenate is formed. This is 
neutralised with hydrochloric acid and filtered through a press in 
order to separate resinous substances which are formed. The 
phenyl arsenic acid in the filtrate is reduced to phenyl arsenious 
oxide by passing a current of sulphur dioxide through. A heavy 
oil deposits at the bottom of the vessel and this is removed by 
decantation and redissolved in 40° Be. sodium hydroxide solution. 
After diluting with 8 cu. m. of water, the solution is cooled to 
15° C. and run slowly into another solution of diazobenzene 
chloride prepared as before. The sodium salt of diphenyl arsenic 
acid which is formed is slightly acidified with hydrochloric acid, 
the diphenyl arsenic acid filtered off and redissolved in 20° Be. 
hydrochloric acid (1 part of the arsenic acid requires 3 parts of 
hydrochloric acid) and the solution obtained is then run into an 
iron vessel, lined internally with tiles. Sulphur dioxide is then 
passed through for 8 hours while the temperature is maintained 
at about 8o° C. Diphenyl chloroarsine then separates as an oil 
which forms a layer at the bottom of the vessel. It is separated 
off and dried in vacuo. 

Physical Properties 

Crude diphenyl chloroarsine is a dark brown liquid which 
gradually turns into a semi-solid viscous mass. 

In the pure state diphenyl chloroarsine forms colourless crystals 
which melt at 41° C. According to some authors it exists in two 
crystalline modifications, the stable one melting at 387° to 
38-9° C. and the labile at 18-2° to 18-4° C.* The labile modification 
is easily converted into the stable form. 2 

1 Somewhat differing values are reported in the literature for the melting point 
of diphenyl chloroarsine : * ' 

37 0 to 38 0 (Lewis and coll., /. Am. Chem. Soc, 1921, 43, 891). 
38° to 39° (Steinkopf and coll., Ber., 1928, 61, 678). 
38-5° to 39° (Fromm and coll., Rec. trav. Chim., 1930, 49, 623). 
40° to 41° (Gryszkiewicz and coll., Bull. soc. chim., 1927, 41, 570). 
40 0 to 42° (Blicke and coll., /. Am. Chem. Soc, 1933, 55, 1161). 
44 0 (Walton and coll., /. Pharmacol., 1929, 35, 241). 
* Gibson and Vining, /. Chem. Soc, 1924, 125, 909. 



DIPHENYL CHLOROARSINE : PROPERTIES 309 

The boiling point at ordinary pressure in an atmosphere of 
carbon dioxide is 333° C. ; at reduced pressures the boiling points 
are as follows : 

MM. MERCURY ° C. 

5 161 (Steinkopf) * 

10 180 (Herbst) 2 

15 185 (Pope and Turner) 

20 193 

30 205 

55 224 

102 245 

The vapour pressure of diphenyl chloroarsine at a temperature t 
may be calculated from the formula (see p. 5) : 

3288 



\ogp = 7-8930 - 



273 + t 



In the following table the values of the vapour pressure are 
given at various temperatures : 

Temperature Vapour Tension 

° C. MM. MERCURY 

O 0-0001 
20 0-0005 
25 0-0007 

45 0-0036 

55 0-0074 

65 0-0146 

75 0-0275 

The volatility of diphenyl chloroarsine at ordinary temperatures 
is very low : at 20 0 C. it is o-68 mgm. per cu. m., while at 98 0 C. 
it is 894 mgm. per cu. m. The specific heat is 0-217 calorie and 
the latent heat of volatilisation is 56-6 calories. 

It has a coefficient of thermal expansion of 0-00075 and a 
specific gravity at 40° C. (solid) of 1-363 and at 45 0 C. (liquid) 
of 1-358. 

It is only slightly soluble in water, 100 ml. dissolving less than 
0-2 gm. However, it is readily soluble in carbon tetrachloride, 
phosgene, chloropicrin and phenyl dichloroarsine. In other 
solvents it dissolves in the following proportions : 

20 gm. in 100 ml. absolute alcohol 
50 „ „ kerosene 
100 „ „ benzene 
14 „ „ olive oil 



1 Steinkopf and coll., Ber., 1928, 61, 678. 

2 Herbst, Kolloidchem. Beihefte, 1926, 23, 340. 



ARSENIC COMPOUNDS 



Chemical Properties 

Water. Water hydrolyses diphenyl chloroarsine, forming 
diphenyl arsenious oxide (m.p. 92-5° to 93*5° C.) : 

2(C 6 H 6 ) 2 AsCl + H 2 0 = [(C.HJtAs]/) + 2HCI. 

According to several authors 1 this reaction is slow at normal 
conditions of humidity, but is considerably accelerated when the 
arsine is brought into contact with aqueous or alcoholic solutions 
of the alkali hydroxides. 2 

This hydrolysis is accelerated by the presence of olive oil or 
turpentine. In the latter case, some oxidation to diphenyl 
arsenic acid takes place (see p. 311). 

Ammonia. With anhydrous ammonia and diphenyl chloro- 
arsine in benzene solution, the following reaction takes place 3 : 

(CeH^sAsCl + 2NH3 = (C 6 H 5 ) 2 AsNH 2 + NH 4 C1. 

Diphenyl arsenamide forms needles melting at 53 0 C. It acts 
on the skin and on the mucous membranes both in solution and 
when dispersed in the air. On exposure to air, it is converted 
into diphenyl arsenious oxide (see above). 

Chlorine. By the action of a solution of chlorine in carbon 
tetrachloride on a solution of diphenyl chloroarsine in chloroform, 
diphenyl trichloroarsine 4 is formed, as crystals melting at 
189 0 C. : 

/CI 

(C 6 H 6 ) 2 As(-Cl 

This trichloro- derivative on treatment with cold water forms 
first the chloride of diphenyl arsenic acid : 

(CeH^sCL, + 2H 2 0 = (C 6 H 5 ) 2 As(OH) 2 Cl + 2HCI, 

which is rapidly converted into diphenyl arsenic acid. 5 According 
to Meyer, diphenyl trichloroarsine has no toxic power. Chlorine 
water also oxidises diphenyl chloroarsine to diphenyl arsenic 
acid. 6 

Bromine. Bromine, in chloroform solution, reacts with diphenyl 
chloroarsine also dissolved in chloroform, forming different 
products according to the amount of bromine : either diphenyl 
chloroarsine bromide, (C 6 H 6 ) 2 AsCl.Br 2 , yellow needles melting 

1 LlBERMANN, loC. dt. 

2 Rona, Z. ges. expt. Med., 1921, 13, 16. 

3 Ipatibv and coll., Ber., 1929, 62, 598. 

4 La Coste and Michaelis, Ann., 1880, 201, 222. 
6 Kappelmeyer, Rec. trav. Chim., 1930, 49, 79. 

» Michaelis, Ann., 1902, 321, 141. 



DIPHENYL CHLOROARSINE : PROPERTIES 311 



at about 158° C, and soluble with partial decomposition in 
benzene 1 ; or diphenyl chloroarsine perbromide, (C 6 H 5 ) 2 AsCl.Br 4 , 
orange-red prisms melting at 146° to 150 0 C. These halogenated 
derivatives lose the atoms of bromine which they contain on 
exposure to moist air. 

Nitric Acid. Diphenyl chloroarsine on heating to about 40° C. 
with concentrated nitric acid is oxidised to diphenyl arsenic acid, 
(C 6 H 5 ) 2 AsOOH. This forms colourless crystals melting at 175° C. 
which are sparingly soluble in hot water, alkalies and alcohol. 
It is not decomposed by nitric acid, nor by boiling chromic acid. 
The copper and lead salts of diphenyl arsenic acid are very 
sparingly soluble in water, even at 100° C. Diphenyl arsenic acid 
dissolves in nitric acid, forming a nitrate of the formula : 

(C 6 H 5 ) 2 AsOOH.HN0 3 . 

Hydrochloric Acid. On boiling diphenyl chloroarsine with 
hydrochloric acid, arsenic trichloride and triphenyl arsine are 
formed, 2 as follows : 

3(C,H ls ) 1 AsCl = AsCL, + 2As(C 6 H 5 ) 3 . 

Chlorosulphonic Acid. Diphenyl chloroarsine, on treatment 
with chlorosulphonic acid forms, besides benzene sulphonyl 
chloride, a chloride of diphenyl arsenic acid having the formula 3 
(C 6 H 6 ) 2 AsOOH.HCl, which forms prisms and melts at 130° C. 

Fluorosulphonic Acid. This converts diphenyl chloroarsine into 
benzene sulphonyl fluoride and the sulphate of diphenyl arsenic 
acid, 2(C 6 H 5 ) 2 AsOOH.H 2 S0 4 , melting at 117 0 C. 

Sodium Iodide. By the action of sodium iodide on diphenyl 
chloroarsine dissolved in acetone, diphenyl iodoarsine 4 is 
obtained : 

(C 6 H 5 ) 2 AsCl + Nal = (CjHJjAsI + NaCl. 

This forms brilliant yellow crystals with m.p. 40-5° C. (or, according 
to Blicke, 5 41° to 42° C), insoluble in water, difficultly soluble in 
cold alcohol, but readily soluble in hot alcohol, ether, acetone, 
benzene, etc. 

Hydrogen Sulphide. On bubbling sulphuretted hydrogen 
through an alcoholic solution of diphenyl chloroarsine, diphenyl 
arsenious sulphide 6 is formed : 

2 (C 6 H s ) a AsCl + H 2 S = [(CgH^s^S + 2HCI. 

1 Rasuvajev, Ber., 1931, 64, 120. 

2 Rasuvajev and coll., /. Obscei Khim., Ser. A' 1932, 2, 529. 
* Steinkopf, Ber., 1928, 61, 678. 

1 Steinkopf and Schwen, Ber., 1921, 54, 1459. 

5 Blicke, loc. cit. 

6 Raiziss and Gavron, Organic Arsenical Compounds, New York, 1923, 216. 



312 



ARSENIC COMPOUNDS 



This forms white acicular crystals at 67 0 C. It is readily soluble 
in benzene, carbon disulphide and chloroform, but sparingly in 
alcohol and ether. This sulphide may also be obtained by the 
action of sodium sulphide on diphenyl chloroarsine in benzene 
solution 1 ; on treatment with mercuric cyanide or silver cyanide, 
diphenyl cyanoarsine is obtained (see p. 314). 

Sodium Thiocyanate. By the action of sodium thiocyanate 
dissolved in acetone on diphenyl chloroarsine dissolved in the same 
solvent, diphenyl thiocyanatoarsine is formed, 2 (C 6 H 5 ) 2 AsSCN, 
an oily, pale brown substance, which is miscible in all proportions 
with benzene and acetone and which decomposes with water, 
giving up the SCN group. It boils at 230 0 to 233 0 C. at 22-23 mm - 
mercury pressure. It reacts quantitatively with sodium 
sulphide 3 : 

afCgH^isAsSCN + NagS = [(C,H s ) t As] f S + aNaSCN. 

Sodium Alcoholate or Phenate. Sodium alcoholate and phenate 
react with diphenyl chloroarsine as follows 4 : 

(C 6 H 6 ).AsCl + C 2 H 5 ONa = (C 6 H 8 ) 2 AsO.C 2 H 8 + NaCl 
(CgH^jAsCl + C 6 H 6 ONa = (CeH^sOXeHs + NaCl 

Methyl Iodide. On heating diphenyl chloroarsine with methyl 
iodide to ioo° C. in a closed tube, a mixture of diphenyl iodoarsine 
(see p. 311) and dimethyl diphenyl arsonium triiodide, 5 
(CH 3 ) 2 (C 6 H 6 ) 2 Asl3, is obtained. 

Acyl Chlorides. When diphenyl chloroarsine is treated with 
one of the aliphatic acyl chlorides, like acetyl chloride, dissolved 
in carbon disulphide and in presence of aluminium chloride, 
acetophenone and arsenic trichloride are formed 6 : 

(C 6 H 5 ) 2 AsCl + 2CH3COCI = 2C 6 H 5 COCH 3 + AsCl 3 . 

Phenyl Ar sines. When diphenyl chloroarsine is treated with 
(mono)phenyl arsine in an atmosphere of nitrogen or carbon 
dioxide, 7 arsenobenzene and tetraphenyl diarsine are formed 8 ; 

4 (C 6 H 5 ) 2 AsCl + 2 C 6 H 5 AsH 2 -> 

C 6 H 6 As=AsC 6 H 5 + 2 (C 6 H 6 ) 2 As-As(C 6 H 6 ) 2 + 4 HC1 

1 Morgan and Vining, /. Chem. Soc, 1920, 117, 777. 

* Steinkopf and W. Mieg, Ber., 1920, 53, 1013. 

* Pancenko and coll., /. Obscei Khim., Ser. A, 1932, 2 193 

* Michaelis, Ann., 1902, 321, 143. ' 

6 Steinkopf and Schwen, Ber., 1921, 54, 1458. 

* Malinovsky, /. Obscei Khim., Ser. A, 1935, 5, 1355, 

7 Steinkopf and Dudek, Ber., 1929, 62, 2494. 

8 Blicke and coll., /. Am. Chem. Soc, 1932, 54, 3353. 



DIPHENYL CHLOROARSINE : PROPERTIES 313 



Tetraphenyl diarsine, or phenyl cacodyl, is also formed by the 
action of diphenyl arsine in ethereal solution on diphenyl 
chloroarsine. It forms crystals melting at 124 0 to 127 0 C. 
(Blicke). 

Chloramine-T . Diphenyl chloroarsine reacts with chloramine-T 
in presence of water to form diphenyl arsenic acid, 1 which 
consists of needles melting at 175° C. (see p. 311). 

When diphenyl chloroarsine is heated, it remains unchanged 
until a temperature of 300 0 to 340° C. is reached, when it becomes 
dark brown and on analysis it is found to have decomposed 
slightly. 

It is not sensitive to detonation and may be employed in 
projectiles. It has no corrosive action on metals such as iron, 
lead, etc. 

Owing to its low vapour tension-, it is necessary, in order to 
utilise it as a war gas, to disperse it in the air as an aerosol 
which contains a high proportion of particles of diameter 
about io -4 to io -5 cm. Such a fine state of subdivision 
can be obtained, according to Prentiss, either by spraying 
solutions of diphenyl chloroarsine in certain solvents, such 
as phosgene, phenyl dichloroarsine, etc., this method being 
employed during the war, or by dispersing it by means 
of explosive charges. In the latter case, the time of 
detonation is too short for an appreciable quantity of 
heat to be transmitted to the diphenyl chloroarsine, and the 
actual dispersion is mainly due to the physical force of the 
explosion. 

In order to attain the degree of subdivision of diphenyl 
chloroarsine, diphenyl cyanoarsine or phenarsazine chloride 
which has been mentioned above, it is first necessary to volatilise 
the substance by some method and then to allow the vapour to 
condense in the air. This is carried out by means of the so-called 
" irritant candles." 

Both in the solid state and the liquid state, and even in the 
form of vapour, diphenyl chloroarsine causes the formation of 
small vesicles on the skin. 2 The minimum concentration causing 
nasal irritation is o-i mgm. per cu. m., according to Miiller, and 
o«5 mgm. per cu. m. according to Prentiss. The maximum 
concentration which a normal man can support for at most 
1 minute is 1-2 mgm. per cu. m. (Flury and Zernick). The 
mortality-product is 4,000 according to Miiller, but Prentiss gives 
15,000 for 10 minutes' exposure. 

1 Burton and Gibson, /. Chem, Soc, 1924, 125, 2275. 
a Hanzlik, (qc. ci(. 



314 



ARSENIC COMPOUNDS 



3. Diphenyl Bromoarsine 



(M.Wt. 309) 




This substance was prepared in 1880 by La Coste and Michaelis, 1 
but was tested as a war gas only in the post-war period. 

Preparation 

According to Steinkopf 2 it may be obtained in the laboratory 
by heating 35 gm. diphenyl arsenious oxide with more than 
I gramme-molecule of hydrobromic acid to 115° to 120° C. for 
4 hours. 

Industrially, diphenyl bromoarsine is prepared by methods 
similar to those described above for the preparation of the 
chloro-compound. That is to say, by the action of arsenic 
tribromide on triphenyl arsine at 300 0 to 350 0 C. or else by the 
diazotisation method, using hydrobromic acid instead of 
hydrochloric acid. 

Physical and Chemical Properties 

Diphenyl bromoarsine forms white crystals and melts at 
54° to 56° C. Its chemical properties are similar to those of 
diphenyl chloroarsine. 

Treated with a solution of chlorine in carbon tetrachloride, 
yellow crystals separate on cooling and these consist of bromo 
dichloro diphenyl arsine, (C 6 H B ) 2 AsCl2Br, and melt at 109 0 to 
116° C. 3 

By the action of bromine on diphenyl bromoarsine in 
chloroform, diphenyl tribromoarsine is formed. This has the 
formula (C 6 H 5 ) 2 AsBr 3 , and forms yellow crystals which melt at 
126 0 C. Excess of bromine forms the perbromide, (C e H 5 ) 2 AsBr 6 , 
orange-red crystals which begin to melt at 115° C. 8 

Diphenyl bromoarsine has similar physiopathological properties 
to the corresponding chloro-compound, but a milder aggressive 
action. 

4. Diphenyl Cyanoarsine (M.Wt. 255) 



Diphenyl cyanoarsine was first prepared by Sturniolo and 
Bellinzoni. 4 

1 La Coste and Michaelis, Ann., 1880, 201, 230. 

* Steinkopf and Schwen, Ber., 1921, 54, 1458. 
3 Kappelmeyer, Rec. trav. Chim., 1930, 49, 77. 

* Sturniolo and Bellinzoni, Boll. Chim. Farm., 1919, 58, 409. 




'^AsCN 



DIPHENYL CYANOARSINE : PREPARATION 315 



It was employed as a war gas towards the end of the war (May, 
1918) both alone and mixed with diphenyl chloroarsine. 

Preparation 

This substance was made during the war 1 by heating potassium 
cyanide with diphenyl chloroarsine : 

(C.HJ.ASC1 + KCN = (C,H 4 ) 1 AsCN + KC1. 

However, it was later 2 discovered that this method of preparing 
diphenyl cyanoarsine had the disadvantage that the product is 
sensitive to alkaline reagents such as sodium or potassium 
cyanide. 

In the other methods worked out since the war, diphenyl 
cyanoarsine is prepared by treating diphenyl arsenious oxide with 
hydrocyanic acid, or by treating either diphenyl chloroarsine or 
diphenyl arsenious sulphide with the cyanide of a heavy metal. 
The reaction between hydrocyanic acid and diphenyl arsenious 
oxide may be carried out at the ordinary temperature 3 or by 
treatment in a closed tube at 100° C. for 2 hours 4 : 

[(C t H i ) i As] 1 0 + 2HCN = 2(C 6 H 6 ) 2 AsCN + H 2 0. 

The reaction with the heavy metal cyanides may be brought 
about either by treating diphenyl chloroarsine at 150° to 160° C. 
for 3 hours with dry, recently prepared silver cyanide, or by the 
treatment of diphenyl arsenious sulphide with mercuric cyanide 
for 2 hours at 160 0 to 200° C. 5 

Laboratory Preparation 

The preparation of diphenyl cyanoarsine in the laboratory may 
be carried out by the action of potassium cyanide on diphenyl 
chloroarsine. 

4-5 gm. potassium cyanide are dissolved in 20-25 ml. water in a 
100 ml. flask and 15 gm. diphenyl chloroarsine are added in small 
portions with continuous stirring. The reaction is exothermic and 
the flask should be cooled externally with water so as to maintain 
the internal temperature at 40 0 to 45 0 C. When the temperature 
commences to fall, the product is allowed to stand. An oil 
separates at the bottom of the flask and is washed with water 
and allowed to crystallise by cooling. The product obtained is 

1 Norris, /. Ind. Eng. Chem., 1919. 11, 826. 

* McKenzie and Wood, /. Chem. Soc, 1920, 117, 406 ; Nenitzescu, Antigaz, 
1929, Nos. 2 and 3. 

8 McKenzie and Wood, /. Chem. Soc, 1920, 117, 413. 

* Steinkopf and Schwen, Bet., 1921, 54, 1460. 

* Morgan and Vining, /. Chem. Soc, 1920, 117, 777. 



3i6 



ARSENIC COMPOUNDS 



further purified by distillation under reduced pressure. The 
yield of diphenyl cyanoarsine by this method is 80-90% of the 
theoretical. 

Steinkopf's method 1 gives higher yields : 

10 gm. of diphenyl arsenious oxide and 6 gm. anhydrous 
hydrocyanic acid (i.e., five times the theoretical amount) are 
placed in a glass tube, which is then sealed in the flame. The 
mixture is then heated for 2 hours at ioo° C. The residue is then 
extracted with ether after cooling, the ether distilled off and the 
product which remains fractionally distilled at reduced pressure 
(13-15 mm.). 

Industrial Manufacture 

In Germany, according to Norris, diphenyl cyanoarsine was 
prepared by treating diphenyl chloroarsine with a concentrated 
aqueous solution of potassium cyanide and heating to 60° C. A 
5% excess of the cyanide was employed and the reaction mixture 
stirred continuously. 

Physical Properties 

Diphenyl cyanoarsine forms colourless prisms with an odour 
of mixed garlic and bitter almonds. It melts at 35° C. (Sturniolo), 
at 32 0 to 34 0 C. (McKenzie), at 31-5° C. (Steinkopf). It boils at 
213° C. at 21 mm. mercury pressure and at 200 0 to 201° C. at 
13 *5 mm. At 760 mm. the boiling point is calculated from the 
vapour pressure curve to be 377° C. 2 The specific gravity is 1*45. 

The vapour pressure is very low and at 20° C. is only 0-0002 mm. 
mercury. The volatility at the same temperature is o-i-o-i5 
mgm. per cu. m. of air. 

Diphenyl cyanoarsine is sparingly soluble in water, but dissolves 
readily in alcohol, benzene, chloroform, ether and ligroin. 

Chemical Properties 

Like diphenyl chloroarsine, diphenyl cyanoarsine is not very 
stable and its arsenic atom has a tendency to change from the 
trivalent to the pentavalent state. 

Water. Atmospheric moisture decomposes diphenyl cyano- 
arsine slowly, hydrocyanic acid and diphenyl arsenious oxide 
being formed : 

2(C 6 H 5 ) 2 AsCN + H 2 0 = [(C,H i ) 1 As],0 + 2HCN. 

1 Steinkopf, Ber., 1921, 54, 1460. 

2 Hkrbst, Kolloidchem. Bethefte, 1926, 23, 340. 



DIPHENYL CYANOARSINE : PROPERTIES 317 



This decomposition takes place more rapidly with hot water, or 
with aqueous or alcoholic solutions of the alkalies. 

The conversion of diphenyl cyanoarsine into diphenyl arsenious 
oxide may be attained also by steam distillation. The oxide 
consists of crystals which are sparingly soluble in water, but 
soluble in alcohol, ether, chloroform ; the melting point is 
92 0 to 93 0 C. 

Chlorine. Diphenyl cyanoarsine in benzene solution is con- 
verted by chlorine into a compound melting at 115 0 C. which, 
according to McKenzie, appears to be anhydride of tetraphenyl 
tetrachloro arsenic acid, [(C e H 5 ) 2 AsCl 2 ] 2 0. The reaction is as 
follows : 

(C 6 H 5 ) 2 AsCN + Cl 2 = (C s H 5 ) 2 As • CN • Cl 2 
(C 8 H 5 ) 2 AsCN • Cl 2 + H 2 0 = (C 6 H 5 ) 2 AsCl 2 • OH + HCN 
2 (C s H s ) 2 AsCl 2 • OH -> H 2 0 + fCaH^As • Cl 2 -0-Cl 2 As-(C 6 H s ) a 

This compound fumes in air and from its aqueous solution 
diphenyl arsenic acid separates on cooling. 

Oxidising Agents. When diphenyl cyanoarsine, cooled in a 
water-bath, is treated with nitric acid, with 2% hydrogen 
peroxide or with bromine water, it is oxidised to diphenyl arsenic 
acid, (C 6 H 6 ) 2 AsOOH which forms acicular crystals melting at 
175° C. The alkali salts of this acid are readily soluble ; the iron 
compound is a white powder which decomposes on heating. 1 

Methyl Iodide. By the action of methyl iodide on diphenyl 
cyanoarsine, by heating in a closed tube for 6 hours at 100° C., 
diphenyl methyl arsonium iodide and triiodide are obtained. 
The latter crystallises in violet needles which melt at 69° C. and 
are insoluble in water and in ether. 

Diphenyl cyanoarsine has such a low vapour pressure that it 
must be diffused as a particulate smoke in the air, in the same 
way as diphenyl chloroarsine. Its behaviour to active carbon is 
due to this state of extreme subdivision. Layers of animal or 
vegetable fibres, properly treated and washed, form an efficient 
filter. 

The minimum concentration of diphenyl cyanoarsine detectable 
by odour is o-oi mgm. per cu. m. according to Lindemann and 
0-005 mgm. per cu. m. according to Meyer. 

A normal man can support a maximum concentration of 
0-25 mgm. per cu. m. of air for not more than 1-2 minutes (Flury). 

1 G. Sturniolo and G. Bellinzoni, Boll. chim. farm., 1919, 58, 409; Gazz, 
chim. ital., 1919, 49, 326. 



3i8 



ARSENIC COMPOUNDS 



The mortality-product is 4,000 according to Muller, or for 10 
minutes' exposure according to Prentiss, 10,000. 

(C) HETEROCYCLIC ARSINES 

The study of the heterocyclic arsines {i.e., those containing the 
atom of arsenic in the nucleus) may be said to have commenced 
only during the war of 1914-18 and led to the discovery of 
substances whose military value is equal, or according to some 
authorities superior, to that of the aromatic arsines. Among 
these substances " Adamsite " has claimed most interest, 
particularly because of the simplicity of its method of preparation. 

This substance, also known as " diphenylamine ckloroarsine," 
has the following structure : 

CI 




N 

I 

H 



which has been confirmed by its mode of formation from arsenic 
trichloride and diphenylamine : 



0 CK CZ) 
+ )As-Cl = HN 
Cr 



<__) 



As-Cl + 2 HC1 



By analogy with other classes of substances of similar constitu- 
tion, such as phenazine (I) and phenoxazine (II) : 



N 



/\/\/\ 



H 

I 

/\A/\ 



N 
I 



II 



THE HETEROCYCLIC ARSINES 319 



it may be accurately described as 10 chloro 5-10 dihydro- 
phenarsazine, or, more briefly, as phenarsazine chloride. 

Various analogous and homologous compounds of phenarsazine 
chloride have been studied. 1 Among the more important may be 
mentioned phenarsazine bromide, obtained by the action of 
arsenic bromide on diphenylamine, 2 phenarsazine iodide 3 and 
phenarsazine fluoride* as well as phenarsazine cyanide. 5 All these 
compounds have toxic properties similar to those of phenarsazine 
chloride. 6 

Substances of analogous types to that of the phenarsazine 
derivatives have also been prepared. Lewis 7 first, and later 
Turner 8 prepared phenoxarsine chloride (6 chlorophenoxarsine) : 

CI 
I 

As 



O 



Kalb 9 prepared arsanthrene chloride : 




CI 



These substances, which are very similar in properties to 
phenarsazine chloride, have the drawback that their preparation 
is in each case very laborious. 

1 Burton and Gibson, /. Chem. Soc, 1924, 2275 ; 1926,464; C. Nenitzescu, 
Antigaz, 1929, Nos. 2-3. 

2 Bayer, D.R.P. 281049. 

3 Rasuvajev and Benediktov, Ber., 1930, 63, 346. 

4 Gibson and coll., Rec. trav. Chim., 1930, 49, 1006. 

5 Gryskiewicz and coll., Bull. soc. chim., 1927, 41, 1323. 
• Gibson and Johnson, /. Chem. Soc, 1931, 2518. 

' Lewis, /. Am. Chem. Soc, 1921, 43, 892. 
8 Turner, /. Chem. Soc, 1925, 127, 544. 
» Kalb, Ann., 1921, 423, 63. 



320 



ARSENIC COMPOUNDS 



Phenarsazine Chloride (Adamsite) (M.Wt. 277 5) 

HN< >AsCl 
X C 6 H 4 / 

According to Hanslian this substance was prepared in Germany 
by Wieland 1 in 1915, and independently in January, 1918, by 
Adams (whence its name of Adamsite). However, the recognition 
of the importance of this substance as a war gas must be attributed 
solely to the English and Americans who studied its chemical and 
biological properties. 

Preparation 

Wieland 2 obtained phenarsazine chloride by treating diphenyl- 
amine with arsenic chloride : 

(C„H 5 ) 2 NH + AsCl 3 = NH(C,H 4 ) t AsCl + 2HCI. 

It may also be obtained by the following methods : 

(a) By heating diphenyl hydrazine with arsenic trichloride. 3 

(b) By boiling aniline with arsenic trichloride, then adding 
sodium hydroxide, and treating the oxide obtained with 
hydrochloric acid. 4 

(c) By treatment of fused diphenylamine with concentrated 
hydrochloric acid and then mixing with arsenious oxide 5 : 

(C 6 H 5 ) 2 NH + HC1 = (C 6 H 5 )gNH • HQ 

2 (C 6 H 5 );>NH • HC1 + As 2 0 3 = 2 NH(C 6 H 4 ),AsCl + 3 H 2 0 

Laboratory Preparation 5 

Contardi's method is used : this involves the treatment of 
diphenylamine with arsenious oxide : 

42 gm. diphenylamine and 21 ml. hydrochloric acid (S.G. 1-19) 
are placed in a porcelain dish of about 300 ml. capacity and 
heated with constant stirring until all the water has been driven 
off. Diphenylamine hydrochloride is obtained as a white powder ; 
it is dried for 2-3 hours at 50 0 to 6o° C. It is mixed with 25 gm. 
arsenious oxide and melted with continuous stirring. When the 
whole mixture is molten, the temperature is gradually raised ; 
at 140° C. the reaction becomes vigorous and water vapour is 
evolved. After 3-4 hours the temperature rises to 200° C. and 

1 Elberfelder Farbenfabrik. Bayer, D.R.P. 281049. 
8 Wieland and Rheinheimer, Ann., 1921, 423, 12. 

3 Lewis and Hamilton, /. Am. Chem. Soc, 1921, 43, 2218. 

4 Burton and Gibson, /. Chem. Soc, 1926, 450. 
1 Contardi, Giorn. Chim. Appl., 1920, 1, 11. 



PHENARSAZINE CHLORIDE: MANUFACTURE 321 



the evolution of water vapour ceases : the reaction may then 
be considered as complete. The product obtained is purified by 
crystallisation from xylene. Yield is almost theoretical. 

Industrial Manufacture 

American Method. The process used by the Americans at 
Edgewood Arsenal for the manufacture of phenarsazine chloride 
is based on the reaction of diphenylamine with arsenic chloride : 

(C 6 H 6 ) 2 NH + AsCl 3 = NH(C 6 H 4 ) 2 AsCl + 2HCI. 

Operating Details. 642 kgm. diphenylamine are first heated to 
150° C. in a large jacketed kettle fitted with an agitator and a 
reflux condenser. 730 kgm. arsenic trichloride (that is, 10% 
excess over theoretical) are added and the heating continued for 
5 hours. During the course of the reaction, the temperature 
rises to 250 0 C, and large quantities of hydrochloric acid are 
evolved. This passes through the condenser and is absorbed in 
water in a special absorption tower. At the end of the reaction, 
the product obtained is transferred to a vessel containing water 
where it is washed, then centrifuged and dried at 30 0 C. Yield 
80%. 

Italian Method. During the war, Professor Contardi proposed 
a method of preparation much more simple than the American 
process just described. In studying a new process for manufactur- 
ing diphenylamine, he observed that the hydrochloride of this 
base is completely dissociated into hydrochloric acid and 
diphenylamine when heated to slightly over 100° C. He studied 
the possibility of using this reaction to prepare phenarsazine 
chloride by starting from arsenious oxide and diphenylamine 
hydrochloride, instead of arsenic trichloride and diphenylamine. 
The equation of this reaction is as follows : 

C H 

2 (C,H i ) i NH-HCl + As.0, = 3 H 2 0 + 2 Hn(* *)as • CI 

In order to prepare phenarsazine chloride by this method it is 
sufficient to mix diphenylamine hydrochloride with arsenious 
oxide and heat to 130° C. After the mixture is melted, the 
temperature is gradually raised to 200° C. When the evolution 
of water ceases, the reaction is complete. Yield 95% of the 
theoretical. 

Fig. 18 shows a diagram of the plant proposed by Professor 
Contardi for the industrial preparation of phenarsazine chloride. 

WAR GASES. H 



322 



ARSENIC COMPOUNDS 



The reaction is carried out in the cast iron kettle A, which 
holds 7-5 litres and is fitted with the helical agitator B which 
imparts an ascending motion to the mass, so that a homogeneous 
distribution of the particles in the liquid is obtained. The kettle 
is closed at the top with a lid, in the centre of which is the agitator 
gear, and which also has a charging hole C for the diphenylamine 
hydrochloride and arsenious oxide. Above this hole a hopper is 

fitted. A stuffing - box 




also passes through the 
lid, supporting the 
thermometer T which 
indicates the temperature 
of the reaction mixture. 
At the bottom of the 
kettle is a tube of 10 cm. 
diameter closed with a 
plug valve D ; through 
this the product is 
discharged. The kettle 
is surrounded by the 
walls L and is heated 
by means of the three 
heating coils f, f, f". 

With a battery of four 
kettles of this description, 
it is possible to make 6 
tons of phenarsazine 
chloride by this method 
in 24 hours. 



Fig. 18. This process differs 

from the American 
method more particularly in saving a considerable proportion of 
the hydrochloric acid (more than two-thirds) and of the arsenious 
oxide, and also makes it unnecessary to prepare arsenic 
trichloride. Moreover, all the difficulties attendant on the 
necessity for utilising or disposing of the large quantities of 
arsenical products which are invariably obtained in the American 
process are obviated. 

Physical Properties 

Phenarsazine chloride in the crude state is a crystalline solid, 
dark green or sometimes brown in colour. It may be obtained 
in the pure condition by crystallisation, or, better, by vacuum 
sublimation. It is then of a canary-yellow colour with a melting 



PHENARSAZINE CHLORIDE: PROPERTIES 323 



point of 189° to I90°C. (Burton and Gibson), 191° to 193 0 C. 
(Rasuvajev), 192-5° (Tanner), 1 or 193° to 195° C. It is practically 
odourless at ordinary temperatures. It has been shown recently 
that phenarsazine chloride, like diphenyl chlorarsine, can exist 
in two modifications : 

A stable orthorhombic form which melts at 195° C, and a 
metastable form which is partly monoclinic and melts at 186° C. 
and partly triclinic, melting at 182° C. 2 

The boiling point calculated from the vapour tension curve 
is 410 0 C. 

The specific heat is 0-268 calorie and the heat of volatilisation 
54-8 calories. 

The volatility at ordinary temperatures is low : at 20 0 C. it 
is only 0-02 mgm. per cu. m. of air. 

The vapour tension at various temperatures is given in the 
following table : 



Temperature Vapour Tension 

°C MM. MERCURY 

o 5 x io- 16 

20 2 X IO -13 

40 2 X IO -11 

IOO 2 X IO" 6 

150 0-003 



The specific gravity at 20° C. is 1-648. It is practically 
insoluble in water, and sparingly soluble in the common organic 
solvents such as benzene, xylene, etc., with which it forms 
molecular compounds of great stability. It is also insoluble in 
phosgene and only slightly soluble at the ordinary temperature 
in carbon tetrachloride. It dissolves in concentrated sulphuric 
acid with an intense cherry-red colour, and in arsenic trichloride 
to give a dark green solution. 



Chemical Properties 

Water. Phenarsazine chloride, unlike the arsenic compounds 
previously described, is slowly hydrolysed by water. On adding 
a little water to the alcoholic solution, a turbidity appears which 
consists of phenarsazine oxide. 3 

Bromine. By the action of bromine on phenarsazine chloride 
in acetic acid solution, a brominated derivative is not obtained, 

1 Tanner, U.S. Pat., 1557384/1922. 

2 Fischer, Mikrachemie, 1932, 12, 257. 

* Kappelmeyer, Rec. trav. Chem., 1930, 49, 82. 

11 — 2 



324 ARSENIC COMPOUNDS 

but the molecule is decomposed and tetrabromodiphenylamine 
is formed 1 : 

Hn( 6 4 )AsCl + 4 Br 2 = HNfCgHaBr^ + AsBr 3 + HC1 + HBr 

n c,h/ 

Tetrabromodiphenylamine forms lustrous crystals melting at 
185 0 to 186 0 C. 

Hydrochloric Acid. When phenarsazine chloride is treated 
with gaseous hydrochloric acid at 160 0 C. it decomposes, forming 
arsenic trichloride and diphenylamine as follows 2 : 

NH( 6 4 )AsCl + 2 HQ = NH(C 6 H 6 ) 2 + AsCl 3 

x c 6 h/ 

Hydriodic Acid. On treatment with aqueous hydriodic acid 
on the water-bath, phenarsazine chloride forms diphenylamine 
as in the previous reaction 3 : 

/C 6 H 4 \ 

NHy yAsCJ + 2 HI = NH (C 6 H 5 ) 2 + AsClI 2 

Alkalies. Phenarsazine chloride reacts with the alkalies to 
form phenarsazine oxide, according to the following equation : 

2 NH( ^As - CI + H 2 0 — 2 HC1 + (HN( /As^O 
C,Hj C 6 H 4 

This substance forms colourless leaflets with a melting point 
above 350 0 C. and is soluble with difficulty in most of the organic 
solvents. It reacts on heating with alcohols and phenols, and 
has a vigorous irritant action. 

Ammonia. When a current of dry ammonia is passed through 
a solution of phenarsazine chloride in xylene, a compound of the 
following composition is obtained : 

/C 6 H 4 \ 

(HN ( rw > AS >3 N 

L 6 H 4 

This is triphenarsazine amine which melts at 295 0 to 300 0 C. 

Oxidising Agents. Oxidising agents react with phenarsazine 
chloride, converting the arsenic atom from the trivalent to the 
pentavalent condition. Hydrogen peroxide in acetic acid 

1 L. Elson and C. Gibson, /. Chem. Soc, 1929, 1080. 

* O. Seide and Gorsky, Ber., 1929, 62, 2187. 

* G. Rasuvajev, Ber., 1931, 64, 2860. 



PHENARSAZINE CHLORIDE: PROPERTIES 325 



solution, 1 for instance, converts phenarsazine chloride to 
phenarsazinic acid : 



This forms acicular crystals melting above 300° C. 

However, nitric acid under certain conditions does not affect 
the arsenic atom, but introduces one or two nitro- groups. These 
groups enter at the ortho- or para- position to the NH — group. 2 
These nitro- compounds have vigorous irritating properties 
according to Libermann. 3 

Sodium Cyanide. Phenarsazine chloride, when treated with 
sodium cyanide in methyl alcohol solution, does not form 
phenarsazine cyanide, but the corresponding methoxy- compound, 



This substance melts at 194 0 C, and on heating with water is 
converted to phenarsazine oxide. 

Phenarsazine cyanide has, however, been prepared by 
Gryskiewicz 4 by treating phenarsazine chloride with- silver 
cyanide. It forms bright yellow crystals which melt at 227° C. 
with decomposition according to Gryskiewicz or at 223° to 224° C. 
according to Gibson. 5 Though it has a more efficient biological 
action than diphenyl cyanoarsine, it is very unstable to heating 
and to explosion. 6 

Potassium Thiocyanate. When phenarsazine chloride is treated 
in acetone solution with an aqueous solution of potassium 
thiocyanate, phenarsazine thiocyanate is formed 7 : 



This forms yellow crystals which melt at 229° to 230° C. 

Chloramine-T. On treatment of phenarsazine chloride in cold 
aqueous alcoholic solution with chloramine-T, 8 phenarsazinic acid 
is formed (see above) . 

1 Wieland and Rheinheimer, Ann., 1921, 423, 7. 

2 Wieland and Rheinheimer, loc. cit. 

» G. Libermann, Khimia i Tecnologia Otravliajuscix Vescestv, Moscow, 1931, 
286. 

* Gryskiewicz, Bull. soc. chim., 1927, 41, 1323. 

6 Gibson and coll., Rec. trav. Chim., 1930, 49, 1006. 

• U. Muller, Militar-Wochenblatt., 1931, 21, 757. 

7 Sergeev and coll., /. Obscei Khim., Ser. A, 1931, 1, 263. 

8 Burton and Gibson, /. Chem. Soc, 1924, 125, 2275. 






326 



ARSENIC COMPOUNDS 



Pyridine. When phenarsazine chloride is treated with boiling 
anhydrous pyridine, triphenarsazine chloride is formed 1 : 



as orange-yellow crystals melting at 260° to 263° C. 

Grignard Reagent. By the action of the Grignard reagent on 
phenarsazine chloride, the corresponding alkyl or aryl derivative 
is formed, i.e.} 



When phenarsazine chloride is heated it begins to melt at 
about 193 0 to 195° C. and remains unaltered until the temperature 
reaches 320° C. when it becomes dark brown. On further heating 
to 370° C, no more decomposition takes place. On cooling 
rapidly it solidifies to a crystalline mass of much darker colour 
than the original substance. 

Unlike diphenyl chloroarsine, phenarsazine chloride attacks 
iron, steel, bronze and copper. 

The minimum concentration causing irritant effect is, according 
to Miiller, o-i mgm. per cu. m. A normal man cannot support a 
concentration greater than 0-4 mgm. per cu. m. for more than 
1 minute. The mortality-index is 30,000 for 10 minutes' exposure 
and 19,500 for 30 minutes' exposure (Prentiss). 

Analysis of the Arsenic Compounds 

Detection 

The presence of the arsenical war gases may be detected by 
applying one of the various methods proposed for detecting 
arsenic in substances. Among these the following, which have 
been much utilised for these compounds, are described : 

Gutzeit Method, Modified by Sanger and Black. 3 This method 
depends on the change of colour, from white to brown, of a paper 
impregnated with mercuric chloride solution when it is exposed 
to the action of hydrogen arsenide. 

In order to use this paper for detecting arsenic compounds, 
the latter must first be converted into arsenious oxide by one of 
the usual decomposition methods (see p. 329 et seq.) and the 

1 Wieland and Rheinheimer, loc. ext. 

% Aeschlimann, /. Chem. Soc, 1927, 129, 413. 

3 Sanger and Black, /. Soc. Chem. Ind., 1907, 26, 11 15 ; Z. anorg. Chem., 
1908, 58, 121. 



HN' 





ARSENIC COMPOUNDS : DETECTION 




oxide then reduced to hydrogen arsenide which can then be 
detected by the Gutzeit test-paper. 

The reaction papers are prepared by repeatedly (four to five 
times) immersing strips of paper in an aqueous 5% mercuric 
chloride solution and allowing them to dry at the ordinary 
temperature. The papers after treatment must be stored away 
from the light in closed 
vessels containing ( 1 

phosphorus pentoxide, 
as they are sensitive 
to light and moisture. 

The procedure to be 
followed in detecting 
the presence of arsenic 
compounds by means 
of these papers is as 
follows : 

A certain quantity 
of the substance to be 
tested 1 is decomposed 
by one of the methods 
described on p. 329 et 
seq., for instance, by 
Ewins's method. The liquid obtained, which contains arsenious 
oxide, is reduced with zinc and hydrochloric acid, using an 
apparatus like that shown in Fig. 19. This consists of a bottle of 
about 30 ml. capacity, fitted with a two-holed stopper, carrying 
a small thistle funnel which passes to within 1 mm. of the bottom 
of the bottle, and a bent tube connected by a rubber stopper 
with another small tube. The latter has a glass bulb of about 

1 The method of taking a sample depends on whether the substance to be 
examined is diffused in the air as vapour or as an aerosol. If the substance is in 
the vapour state, a part of the sample is passed through a U tube filled with dry, 
finely divided silica gel. Then the material absorbed on the silica is decomposed 
by one of the methods described on p. 329 et seq., and the solution obtained 
is tested by the Gutzeit method. 

If the substance is in the form of an aerosol, the sample must be passed through 
one of the following ; 

(a) A wash-bottle with a porous partition containing a solvent as ether, 
benzene, acetone, etc. (Labat and Dufilho, Bull. soc. pharm. Bordeaux, 1933, 
71, 113). 

(6) A glass tube filled with compressed cotton-wool. 

(c) A glass tube filled with about 4 cm. anhydrous sodium sulphate held 
between two layers of cotton wool. 

The solution obtained by method (a), or the material obtained by method (6) 
or (c), is treated by one of the methods described on p. 329 et seq. to convert the 
arsenic present to the oxide, and then the Gutzeit method is used. It is simpler, 
however, to treat the solution from (a), or an alcoholic extract of the materials 
from (6), or (c) directly in the Gutzeit apparatus with zinc and sulphuric acid, 
in presence of copper sulphate or better a few drops of platinic chloride solution. 



Fig. 19- 



ALIPHATIC ARSENIC COMPOUNDS : DETECTION 329 



an aqueous solution of hydrogen sulphide. In presence of a 
chloroarsine an opalescence or a white amorphous precipitate 
forms in a few minutes, according to the concentration of the 
chloroarsine in the sample. 

In the presence of £ chlorovinyl dichloroarsine an excess of 
hydrogen sulphide should be avoided or the sulphide will be 
decomposed. The sensitivity is 0-02-0-05 mgm. of chloroarsine. 
The sensitivity is greater if the chloroarsines are in aqueous 
solution than if they are in alcohol. 

Detection of Methyl Dichloroarsine 

On adding a few drops of an aqueous solution of mercurous 
nitrate, faintly acid with nitric acid, to a solution containing 
methyl dichloroarsine, a grey precipitate of metallic mercury is 
formed. 

Sensitivity : 1 mgm. of methyl dichloroarsine. 

Detection of Ethyl Dichloroarsine 

When a solution of ethyl dichloroarsine is treated with an 
aqueous solution of mercurous nitrate, acidified with nitric acid, a 
white precipitate forms, and this changes to grey in a few seconds. 

Sensitivity : a turbidity is easily visible in the presence of 
2-5 mgm. ethyl dichloroarsine. 

The limit is 1 mgm. 

Detection of /? Chlorovinyl Dichloroarsine 
When a few drops of mercurous nitrate solution, slightly 

acidified with nitric acid, are added to a solution containing 

j3 chlorovinyl dichloroarsine, a white precipitate forms which 

turns grey within 12 hours. 
Sensitivity : 1 mgm. j3 chlorovinyl dichloroarsine. 

Detection of Phenarsazine Chloride 

On heating a solution containing phenarsazine chloride with 
an aqueous solution of hydriodic acid on the water-bath, 
diphenylamine is formed (see p. 324), which can be distilled off 
in a current of steam and detected by means of the well-known 
reaction with nitric acid in sulphuric acid solution. 

Quantitative Determination 

The quantitative determination of the arsenical war gases is 
usually carried out by decomposing the substance by one of 
the usual methods and then determining the arsenic either 
gravimetrically or volumetrically. 

Method of the German Pharmacopoeia. 0-2-0-3 gm. of the 
substance is boiled for about 1 hour with 10 ml. concentrated 



33o 



ARSENIC COMPOUNDS 



sulphuric acid and i ml. fuming nitric acid in a narrow-mouthed 
flask of Jena glass. After cooling and adding 50 ml. water, the 
solution is evaporated and the above treatment repeated. 10 ml. 
water, 2 gm. potassium iodide and sufficient water to dissolve the 
precipitate are then added in succession to the cooled solution. 
After allowing to stand* for about \ hour, the iodine liberated 
is titrated without using any indicator. 

Ewins's Method. 1 0-1-0-2 gm. of the substance is mixed in a 
300 ml. Kjeldahl flask with 10 gm. potassium sulphate, 0-2-0-3 gm. 
starch and 20 ml. concentrated sulphuric acid. This mixture is 
then heated by means of a Bunsen burner, first moderately for 
10-15 minutes, then more vigorously for about 4 hours, until 
decomposition is complete. The liquid is cooled, transferred to a 
350 ml. flask and made alkaline to litmus paper with sodium 
hydroxide. It is then cooled to 30 0 to 40 0 and sulphuric acid 
added drop by drop until the solution is faintly acid. A saturated 
solution of sodium bicarbonate is then added until the solution is 
again alkaline, 5-10 ml. being added in excess. The arsenious 
acid formed is then titrated with iodine solution using starch as 
indicator. 

Robertson's Method? This method consists synoptically of the 
following phases : 

(a) Decomposition of the substance with sulphuric-nitric acid 
mixture. 

(b) Elimination of the nitrous compounds with ammonium 
sulphate. 

(c) Titration of the arsenite formed with iodine. 

0-2 gm. of the substance is weighed into an Erlenmeyer flask 
and heated for about an hour with 5 ml. concentrated sulphuric 
acid and 1 ml, fuming nitric acid. After cooling the flask 
cautiously, a further 10-15 drops of fuming nitric acid are added 
and the flask again heated for 5 minutes to ensure complete 
decomposition. 1 gm. solid ammonium sulphate is then added 
and the contents of the flask agitated well until all the nitrogen 
has been evolved. They are then cooled and diluted with 60-70 ml. 
water. 1 gm. potassium iodide is then added and a few fragments 
of porous plate. A pear-shaped bulb of glass is placed in the 
mouth of the flask and the liquid concentrated to 40 ml. The 
iodine which is liberated is then decolorised with N/100 thio- 
sulphate and the solution diluted to 100-120 ml. with cold water. 
The whole is then transferred to a 500 ml. flask containing 50 ml. 

1 Ewins, /. Chem. Soc, 1916, 109, 1355. 

* Robertson, /. Am. Chem. Soc, 1921, 43, 182. 



ALIPHATIC ARSENIC COMPOUNDS 



4 N sodium carbonate solution and the remaining acid neutralised 
with a slight excess of sodium bicarbonate. Starch solution is 
added and the arsenite present titrated with iodine. 

Rogers's Method. 1 This method is based on the decomposition 
of the arsenical compound with nitric acid and ammonium 
persulphate and the titration of the iodine liberated on addition 
of potassium iodide. 

About 0-5 gm. of the substance is weighed accurately into a 
500 ml. flask and 10 ml. water and 5 ml. nitric acid are added. 
The mixture is then heated, ammonium persulphate being added 
until the solution becomes clear. If the liquid persistently 
remains yellow, showing that the substance is refractory, it is 
boiled for several minutes with a few ml. water and several gm. 
of ammonium persulphate. 

The solution is then diluted with 100 ml. water, treated with 
about 5 ml. of a saturated solution of acid sodium ammonium 
phosphate and then an excess (about 40 ml.) of magnesia mixture 
added. A precipitate forms and is dissolved in dilute nitric acid ; 
the solution is then heated to boiling, an excess of ammonia 
added, and it is then allowed to stand for about 2 hours. The 
precipitate is filtered off, washed with dilute ammonia and 
dissolved in 70 ml. dilute hydrochloric acid (3:2). 

To the acid solution 3 gm. of potassium iodide in 6 ml. water 
are added and 70 ml. water. The liberated iodine is then titrated 
with sodium thiosulphate. 

Direct methods of estimation have been proposed for certain 
of the war gases. Some of these are described below. 

Determination of the Aliphatic Arsines 

Jurecev 2 suggested the following method for the determination 
of the aliphatic arsines present in vapour form in the air. 

A known volume of the air is passed through a U tube filled 
with dry, fine-grained silica gel. The silica gel with the substance 
absorbed on it is transferred to a nickel or silver crucible and 
covered with a layer of magnesium oxide which is well pressed 
down. 6 gm. of a mixture of equal parts of sodium peroxide and 
sodium carbonate are added and pressed down, and this is finally 
covered with a layer of sodium carbonate. The crucible is 
heated with a small flame for about 15 minutes until the bottom 
is dull red. It is then allowed to cool and placed in a beaker, hot 
water is added and the beaker warmed on the water-bath. The 
solution is neutralised with dilute sulphuric acid and warmed 

1 Rogers, Canad. Chem. J., 1919, 3, 398. 

* Jurecev, Coll. trav. chim. Czech., 1934. •>> 468. 



332 



ARSENIC COMPOUNDS 



again on the water-bath to decompose the hydrogen peroxide 
present. The silica gel is filtered off and washed with hot water, 
then the liquid is allowed to cool, made up to a convenient 
volume and the arsenic determined in an aliquot by the colori- 
metric 1 method using mercuric chloride paper (see p. 326). 

Determination of Methyl Dichloroarsine 

For this determination, the following method has been 
recommended by Uehlinger and Cook 2 : 

5 gm. of the methyl dichloroarsine are treated with 200 ml. 
water and the hydrochloric acid formed by the hydrolysis 
neutralised to litmus. Sodium bicarbonate is then added and the 
solution titrated with a decinormal iodine solution. 

Determination of /? Chlorovinyl Dichloroarsine 

This determination is usually carried out by the method of 
Lewis and Perkins, 3 in which the /? chlorovinyl dichloroarsine is 
decomposed by 15% sodium hydroxide solution at a temperature 
below 37° C. Acetylene is evolved quantitatively. 




Fig. 20. 

0-2-0-4 gm. of the substance is weighed into a flask B (Fig. 20) 
of 50 ml. capacity, and 5 ml. of 15% sodium hydroxide solution 
are introduced from the burette A , the liquid then being warmed 
to about 37° C. The decomposition of the /? chlorovinyl 
dichloroarsine is complete after 15 minutes' agitation and then 
the volume of acetylene formed is read off in the burette C. From 
this the quantity of fi chlorovinyl dichloroarsine in the sample 

1 K. Uhl, Z. angew. Chem., 1937, 50, 164. 

2 Uehlinger and Cook, /. Ind. Eng. Chem , 1919, 11, 105. 

3 Lewis and Perkins, Ind. Eng. Chem., 1923, 15, 290. 



ARSENIC COMPOUNDS: DETERMINATION 333 



can be calculated. The U tube contains 15% sodium hydroxide 
solution which ensures the complete decomposition of the sample. 

Determination of Chlorovinyl Arsines 

In order to determine the amount of each constituent in a 
mixture of the chlorovinyl arsines, the method proposed by 
Brinton 1 may be employed. This utilises the following reactions : 

(1) Cold water hydrolyses 

3 chlorine atoms in arsenic trichloride, 
2 „ „ p chlorovinyl dichloroarsine, 

and 1 „ „ pp' dichlorovinyl chloroarsine. 

(2) By prolonged heating with alcoholic soda all four compounds 
are attacked with the formation of 3 molecules of sodium chloride 
from each. 

(3) A solution of sodium bromate in dilute hydrochloric acid 
oxidises the arsenic trichloride and /? chlorovinyl dichloroarsine 
to the pentavalent state. 

(4) Moderate boiling with 15% sodium hydroxide causes the 
attack of both P chlorovinyl dichloroarsine and PP' dichlorovinyl 
chloroarsine, but not trichlorovinyl arsine, with formation of 
sodium arsenite which may be titrated with sodium bromate after 
acidification. 

Determination of Phenyl Dichloroarsine 

Fleury's 2 method may be employed for this determination ; it 
consists in hydrolysing the sample with water and titrating the 
oxide formed with iodine solution. The following reaction takes 
place : 

/OH 

C s H 8 -AsCl a + I, + 3 H 2 0 = C 6 H 8 Asf=0 + 2 HI + 2 HC1 

^ OH 

A sample of phenyl dichloroarsine is weighed accurately, 
treated with water and alcohol and then titrated, without adding 
any sodium bicarbonate, with a decinormal solution of iodine, 
until the yellow colour is permanent. The number of ml. of 
iodine solution employed multiplied by 0-01115 gives the amount 
of phenyl dichloroarsine (in gm.) in the sample. 

Determination of Diphenyl Chloroarsine 

Fleury's method, depending on the same principle as the 
preceding estimation, is most frequently employed for the 

1 Chemical Welfare Communication, 1923 (see Ind. Eng. Chem., 1923, 15, 290). 
8 P. Fleury, Bull. soc. chim., 1920, [4] 27, 49°. 699. 



334 



ARSENIC COMPOUNDS 



determination of diphenyl chloroarsine. The titration must be 
carried out in benzene or chloroform solution, however, and not 
in aqueous alcoholic solution, and in presence of sodium 
bicarbonate, which accelerates the velocity of the reaction and 
also dissolves the diphenyl arsenic acid which is formed : 

(CjHJjAsCl + I 2 + 2H 2 0 = (C 6 H 6 ) 2 AsOOH + 2 HI + HC1. 

The sample (0-2-0-4 gm.) is weighed accurately and dissolved 
in 10-15 ml. chloroform or benzene, 20 ml. of a saturated solution 
of sodium bicarbonate are added and the liquid is then titrated 
with N/10 iodine solution, being shaken vigorously after each 
addition of iodine. The end of the titration is shown by the 
appearance of a violet colouration in the solvent. The number of 
ml. of N/10 iodine solution employed multiplied by 0-0132 gives 
the amount of diphenyl chloroarsine present in the sample, in gm. 

In order to determine the amount of diphenyl chloroarsine in 
air, Sieverts 1 recommends the following method (cp. note, 

P- 327)- 

A sample of the air is taken in a glass flask of 10-15 litres 
capacity and washed three times with 30 ml. benzene ; the 
benzene solutions are evaporated together on the water-bath to a 
volume of 10-20 ml. and then titrated with a N/1,000 solution 
of iodine as described above. The number of ml. of iodine 
employed multiplied by 0-132 gives the amount of diphenyl 
chloroarsine present in the sample of air. 

This method is not specific, however, nor is it sufficiently 
sensitive ; it also suffers from the inconvenience attendant on 
the instability of millinormal solutions of iodine. 

It is better to use Jurecev's 3 method for this estimation ; it 
consists in passing a known volume of the aerosol (e.g., 50 litres) 
through a wash-bottle with a porous partition containing ether. 
The solvent is then evaporated off on the water-bath, the residue 
decomposed by one of the methods described on p. 329 et seq., 
and the arsenic determined colorimetrically by means of mercuric 
chloride paper (see p. 326). 

Determination of Diphenyl Cyanoarsine 

Diphenyl cyanoarsine may be estimated in the same manner as 
diphenyl chloroarsine, by titration with iodine (Sieverts) : 

(C 6 H s ) 2 AsCN + 2 H 2 0 +I 2 = (CgH^aAsOOH + 2HI +HCN. 
A sample of the air to be analysed is introduced into a glass 

1 A. Sieverts, Z. angew. Chem., 1922, 35, 17. 
! Jurecev, Coll. trav. chim. Czech., 1934, 6> 468. 



ARSENIC COMPOUNDS : DETERMINATION 335 



flask, as in the case of diphenyl chloroarsine, and washed with 
alcohol (not benzene, for in the latter solvent diphenyl cyanoarsine 
does not react with iodine) . The alcoholic solution is diluted with 
an equal volume of water and about 5 ml. benzene are added. 
The diphenyl cyanoarsine reacts quantitatively with iodine in the 
aqueous alcoholic solution, while the excess of iodine passes into 
the benzene layer. 

The number of ml. of N/1,000 iodine employed multiplied by 
0-127 gives the quantity of diphenyl cyanoarsine in the sample 
of air taken, in mgm. 

It is advisable to carry out a blank determination. 

Determination of Phenarsazine Chloride 

A known volume of air containing the substance to be examined, 
in the form of an aerosol, is passed through a wash-bottle with a 
porous partition, of the type recommended by Kolliker, 1 
containing ether. 

The solvent is removed on the water-bath, the residue is 
oxidised by means of a mixture of concentrated sulphuric acid, 
concentrated nitric acid and hydrogen peroxide, according to 
Winterstein's method, 2 and the arsenic is determined in the 
solution obtained by the colorimetric method with mercuric 
chloride paper (see p. 326). 

Determination of Arsenic Trichloride in Phenyl 
Dichloroarsine 

Fleury recommends the following method for the determination 
of the arsenic chloride present in a sample of phenyl dichloroarsine. 

A known amount of the sample (equivalent to about 30 ml. 
N/10 iodine solution) is dissolved in 15-20 ml. 95% alcohol 
and titrated directly with iodine without addition of sodium 
bicarbonate. An excess of a saturated solution of sodium 
bicarbonate is then added ; if after this the solution absorbs 
more iodine, the presence of arsenic trichloride is indicated, and 
from the number of ml. of iodine solution absorbed in these 
conditions, the quantity of arsenic trichloride present in the 
sample may be calculated. 

According to Delepine, 3 this method may also be employed for 
the determination of the arsenic trichloride present in the aliphatic 
arsines. 

1 Kolliker, Chem. Fabrik., 1932, 5, 1 ; 1933. 6, 299. 

2 Winterstein, Mikrochemie., 1926, 4, 155. 

8 Delepine, Rapport a I'Insp. Etudes et Expdr. Chim., 26, 10, 918. 



Table XIII. Table of Conversion for Gas Concentrations : parts per 



M.Wt. 


1 mgm,/l. 
ppm. 


1 ppm. 
mgm./l. 


M. Wt. 


1 mgm./l. 
ppm. 


1 ppm. 
mgm./l. 


M.Wt. 


i mgm./l. 
ppm. 


I DDm. 
mgm./l. 








51 


479 


0.O02086 


101 


242.1 


0.004I3 


2 


12 23O 


0.0000818 


52 


470 


.002127 


102 


239-7 


.00417 


3 


8 150 


.0001227 


53 


461 


.002168 


103 


237-4 


.00421 


4 


6 113 


.0001636 


54 


453 


.002209 


104 


235-1 


.00425 


5 


4 890 


.0002045 


55 


445 


.002250 


105 


232.9 


.00429 


6 


4 °75 


.0002454 


56 


437 


.002290 


106 


230.7 


•00434 


7 


3 493 


.0002863 


57 


429 


.002331 


107 


228.5 


.00438 


8 


3 056 


.000327 


58 


422 


.002372 


108 


226.4 


.00442 


9 


2 717 


.000368 


59 


414 


.002413 


109 


224-3 


.00446 


io 


2 445 


.000409 


60 


408 


.002554 


HO 


222.3 


.00450 


11 


2 223 


.000450 


61 


401 


.002495 


111 


220.3 


.00454 


12 


2 038 


.000491 


62 


493 


.OO254 


112 


278.3 


.00458 


13 


1 881 


.000532 


63 


388 


.00258 


113 


216.4 


.00462 


14 


1 746 


.000573 


64 


382 


.00262 


114 


2145 


.00466 


15 


1 630 


.000614 


65 


376 


.00266 


115 


212.6 


.00470 


16 


1 528 


.000654 


66 


37° 


.00270 


116 


2I0.8 


•00474 


17 


1 438 


.000695 


67 


365 


.00274 


117 


209.O 


.00479 


18 


1 358 


.000736 


68 


360 


.00278 


ll8 


207.2 


•00483 


19 


1 287 


.000777 


69 


354 


.00282 


U9 


205.5 


.00487 


20 


1 223 


.000818 


70 


349 


.00286 


120 


203.8 


.00491 


21 


1 164 


.000859 


71 


344 


.00290 


121 


202.1 


■00495 


22 


1 111 


.000900 


72 


34° 


.00294 


122 


2OO.4 


.00499 


23 


1 063 


.000941 


73 


335 


.00290 


123 


I98.8 


•00503 


«4 


1 019 


.000982 


74 


33° 


•00303 


124 


192.7 


.00507 


25 


978 


.001022 


75 


326 


.00307 


125 


195-6 


.00511 


26 


940 


.001063 


76 


322 


.00311 


126 


194-3 


•00515 


27 


906 


.001 104 


77 


318 


•00315 


127 


192.5 


.00519 


28 


873 


.001145 


78 


313 


.00319 


128 


191 -0 


.00524 


29 


843 


.001186 


79 


3°9 


•00323 


129 


189.5 


.00528 


30 


815 


.001227 


80 


306 


.00327 


130 


188.1 


■00532 


31 


789 


.001286 


81 


302 


00331 


131 


186.6 


•00536 


32 


764 


.001309 


82 


298 


•00335 


132 


185.2 


.00540 


33 


741 


.001350 


83 


295 


•00339 


133 


183.8 


.00544 


34 


719 


.001391 


84 


291 


.00344 


134 


182.5 


.00548 


35 


699 


.001432 


85 


288 


.00348 


135 


181.1 


•00552 


36 


679 


.001472 


86 


284 


•00352 


130 


179.8 


.00556 


37 


661 


.001513 


87 


281 


.00356 


137 


178.5 


.00560 


38 


643 


.001554 


88 


278 


.00360 


138 


177-2 


.00564 


39 


627 


.001595 


89 


275 


.00364 


139 


175-9 


.00569 


40 


611 


.001636 


90 


272 


.00368 


I40 


174.6 


■00573 


41 


596 


.001677 


91 


269 


.00372 


1 4 1 


173-4 


.00577 


42 


582 


.001718 


92 


266 


.00376 


I42 


172.2 


.00581 


43 


569 


.001759 


93 


263 


,00380 


143 


171.0 


.00585 


44 


556 


.001800 


94 


260 


.00384 


I44 


I69.8 


.00589 


45 


543 


.001840 


95 


257 


.00389 


145 


168.6 


.00593 


46 


532 


.001881 


96 


255 


•OO393 


I46 


167.5 


.00597 


47 


520 


.001922 


97 


252 


•00397 


147 


I66.3 


.00601 


48 


5°9 


.001963 


98 


249-5 


.00401 


I48 


162.5 


.00605 


49 


499 


.002004 


99 


257.0 


.00405 


149 


164.I 


.00609 


SO 


489 


.002045 


100 


244-5 


.OO409 


150 


I63.O 


.00613 



336 



million into mgm. per litre and vice versi (25 0 C. and 760 mm. mercury) 



M.Wt. 


1 mgm./l. 
ppm. 


i ppm. 
mgm./l. 


M. Wt. 


1 mgm./l. 
ppm. 


1 ppm. 
mgm./l. 


M.Wt. 


1 mgm./l. 
ppm. 


1 ppm. 
mgm./l. 


151 


161.9 


0.00618 


201 


121.6 


0.00822 


251 


97-4 


0.01027 


152 


160,9 


.00622 


202 


121.0 


.00826 


252 


97.0 


.01031 


153 


159-8 


.00626 


203 


120.4 


.00830 


253 


96.6 


•°'°35 


154 


158.8 


.00630 


204 


119.9 


.00834 


254 


96.3 


.01039 


155 


157-7 


.00634 


205 


119-3 


.00838 


255 


95-9 


•01043 


156 


156.7 


.00638 


206 


118.7 


.00843 


256 


95-5 


.01047 


157 


155-7 


.00642 


207 


118.1 


.00847 


257 


95-1 


.01051 


158 


154-7 


.00646 


208 


117.5 


.00851 


258 


94.8 


•01055 


159 


153-7 


.00650 


209 


117.0 


.00855 


259 


94-4 


.01059 


160 


152.8 


.00654 


210 


116.4 


.00859 


260 


94 -o 


.01063 


161 


151.9 


.00658 


211 


115.9 


.00863 


261 


93-7 


.01067 


162 


150-9 


.00663 


212 


115-3 


.00867 


262 


93-3 


.01072 


163 


150-0 


.00667 


213 


114.8 


.00871 


263 


93° 


.01076 


164 


149.1 


.00671 


214 


114-3 


.00875 


264 


92.6 


.0I080 


165 


148.2 


.00675 


215 


113-7 


.00879 


265 


92.3 


.01084 


166 


147-3 


.00679 


216 


113.2 


.00883 


266 


91.9 


.01088 


167 


146.4 


.00683 


217 


112.7 


.00888 


267 


91.6 


.01092 


168 


145-5 


.00687 


218 


112.2 


.00892 


268 


91.2 


.01096 


169 


144-7 


.00691 


219 


111.6 


.00896 


269 


90.9 


.01100 


170 


143-8 


.00695 


220 


ill. I 


.00900 


270 


90.6 


.01104 


171 


143-0 


.00699 


221 


110.6 


.00904 


271 


90.2 


.01108 


17a 


142. 2 


•00703 


222 


110.1 


.00908 


272 


89.9 


.01112 


173 


141.3 


.00708 


223 


109.6 


.00912 


273 


89.6 


.01117 


174 


140.5 


.00712 


224 


109.2 


.00916 


274 


89.2 


.01121 


175 


139-7 


.00716 


225 


108.7 


.00920 


275 


88.9 


.01125 


176 


138-9 


.00720 


226 


108.2 


.00924 


276 


88.6 


.01129 


177 


136.1 


.00724 


227 


107.7 


.00928 


277 


88.3 


•01133 


178 


137-4 


.00728 


2?8 


107.2 


•00933 


278 


87.9 


.OU37 


179 


136.6 


.00732 


229 


106.8 


•00937 


279 


78.6 


.0II4I 


180 


135-8 


.00736 


230 


106.3 


.00941 


280 


87-3 


.OU45 


181 


135-1 


.00740 


231 


105.8 


.00946 


281 


87.0 


.OII49 


183 


134-3 


.00744 


232 


1054 


.00949 


282 


86.7 


.OU53 


183 


133-6 


.00748 


233 


104.9 


.00953 


283 


86,4 


.OII57 


184 


132-9 


•00753 


234 


104.5 


•O0957 


284 


86.1 


.01 162 


185 


132.2 


.00757 


235 


104.0 


.00961 


285 


85.8 


.OII66 


186 


131-5 


.00761 


236 


103.6 


.00976 


286 


85-5 


.OII70 


187 


130.7 


.00765 


237 


103.2 


.00969 


287 


85.2 


.OII74 


188 


130.1 


.00769 


238 


102.7 


•00973 


288. 


84.9 


.01178 


189 


129.4 


■00773 


239 


102.3 


.00978 


289 


84.6 


.01182 


190 


128.7 


.00777 


240 


101.9 


.00982 


290 


84-3 


.OI186 


191 


128.0 


.007&1 


241 


1*1.5 


.00986 


291 


84.0 


.01 190 


192 


127-3 


.00785 


242 


101.0 


.00990 


292 


83-7 


.01194 


193 


126.7 


.00789 


243 


100.6 


.00994 


293 


83-4 


.OII98 


194 


126.0 


•00793 


244 


100.2 


.00998 


294 


83.2 


.01202 


195 


125-4 


.00798 


245 


99.8 


.01002 


295 


82.9 


.01207 


196 


124.7 


.00802 


246 


99-4 


.01006 


296 


82.6 


.01211 


197 


124.1 


.00806 


247 


99 0 


.01010 


297 


82.3 


.OI2I5 


198 


123-5 


.00810 


248 


98.6 


.01014 


298 


88.0 


.OI219 


199 


122.9 


.00814 


'249 


98.2 


.01018 


299 


81.8 


.01227 


200 


122-3 


.00818 


250 


97- 8 


.01022 


300 


81.5 


.01227 



337 



Table XIV. List of the Most Important War Gases Employed 



2 


3 


Military Name 




7 


8 


Name 


Formula 


4 


5 




M Wt 


M Pt 






French 


German 


USA 




°C 


Ethyl bromoacetate 


r*U TJ»- T-J 








167 


— 


Xylyl bromide 


C« rl 1 1 On i ) Oh, dT 




1 -o ton 




i Re 

1°5 




Chloroace tone 


TT r*f\ f^ZJ r*1 

Cxi B — CO — Cri,Cl 


Tonite 


A-Mon 




92 5 




Benzyl bromide 


C.H,CH,Br 


Cychte 


T- Stoff 




171 


4 


Benzyl iodide 


OerisCtia 1 


Fraisimte 






2 1 o 


2 4 


Chlorine 


CI, 


Bertholite 


Chlor 




71 


— 102 


Bromine 
Ethyl 

chlorosulphona te 
jvietnyi 

chlorosulphona te 


Br, 




Brom 




159 8 


— 7 


ClSO s OCiH 8 


Sulvirute 


— 




144 5 




CISOtOCHi 


vulantite 


C-Stoff 




130 5 


— 70 


Monochlorome thy 1 














chloroformate 


CI — COO — CH,C1 








129 




Bromoacetone 


f> T_T i"/** PTI Tl- 

Cxi, — CO — c±i,fc>r 




B-Stoff 


BA 


136 5 


—54 


Bromomethylethyl 










ketone 


r* T_T f~Tk C T_T T3f 

L/jxlj — IU — Cxia-tSr 


Homomartorute 


Bn Stoff 




151 




Dimethyl sulphate 


bOifOCH,), 




D Stoff 




126 


—31' 


Perchloromethyl 


Clairsite 










mercaptan 


CC1,— S— CI 







186 





Phosgene 


coa, 


Collongite 





CG 


99 


-118 


Ethyl lodoacetate 


CHJ— COOC.H. 









214 




Acrolein 


Cxij = Cri — CtiO 


Papite 







56 


— 88 


Tnchlorome th yl 










chloroformate 




Surpalite 


Perstoff 




198 


— 57 


Hydrocyanic acid 


HCN 


Fores tite 






27 


— 15 


Chloropicrin 


CC1 8 — JNU| 


Aquinite 


Klop 




164.5 


— 69 


Cyanogen chloride 


C1CN 


Mauguinite 


— 




01 4 


-6 


Cyanogen bromide 


TJ— XT 




E Stoff 




106 




Phenylcarbylamme 












chloride 


C,H,NCCli 


— 


K Stoff 





175 


— 


Dichloroethyl 




Ypente 








sulphide 

urpnenyl 

chloroaisine 


S(CH,— CH.Cl), 


Lost 


HS 


159 


14 


(C.H.J.AsCl 




Clark I 


DA 


264 5 


41 












dichloroaisine 


C.H,Asa, 








223 


— 20 


Dichloromethyl 




Cici 










ether 


o(CH,a), 






114 7 




Dibromomethyl 


Bibi 










ether 


O(CH.Br), 






204 


-34 


Ethyl 










dichloroarsine 


C,H 5 AsCl, 




Dick 


ED 


175 


-65 


Thiophosgene 


CSC1, 


Lacnmite 






115 




Diphenylcyano 














arsine 


(C.H,),AsCN 




Clark II 


CDA 


255 


31 


Methyl 












dichloroarsine 


CH.AsCl 




Methyldick 


MD 


161 


-42- 



Column 1. The dates are quoted from Hansllan, Der Chemische Krteg, Berlin, 1927. 
Column 13. See p 6. 

Column 16. Lower Limit of Irritation : the minimum concentration (in mgm. per cu. m ) causing irritation (Fries , Vedder; 
MuUer). 



338 



in the War of 1914-18, in Chronological Order of their first use 



9 


10 


11 

Vap. 


12 

Vap. 


13 

Volatility 
at 20° C. 
mgm./cu. m. 


14 

Coeffic. 


! 15 

Princ. biolog. 


16 


17 


Mortality-product 


B. Pt. 
°C. 


S.G. 


den. 
air = 1 


Press, 
mm. Hg. 


thermal 
expansn. 


IXI 


LI 


18 

German data 


19 
American 
data 


168 
210—220 
119 
199 
226 
-335 
59 


1-53 

i'4 

1-16 

1-43 

1-77 

1-4 

31 


5'8 

3-2 
5-8 
7-5 
2-5 
5-5 




— 

172 




600 
61,000 
2,440 
1,200 






0-0021 


Lachrym. 
,» 

Suffoc. 
Toxic 


10 

1-8 
18 

4 
2 

10 


40 
15 

loo 
60 
30 

loo 


3,000 
6,000 
3,000 
6,000 
3,000 
7,500 


23,000 
56,000 
23,000 
45,000 
30,000 
56,000 


152 


1-4 


5 




18,000 




Lach. Suf. 


2 


50 


3,000 


10,000 


133 


1-49 


4-5 




6o,00O 




,, 


2 


40 


2,000 


20,000 


106-5 
136 


1-46 
l-6 3 


4-5 
4-7 


56 
9 


75,000 







2 
1 


50 
IO 


4,000 


10,000 
32,000 


145 
188 


1-43 
1-33 


52 
4-3 


— 


3.300 





Tox'.' Ves. 


1-6 


II 

50 


6,000 
1,500 


20,000 
5,000 


148 

8-2 

179 
52 


1-7 
1-4 
1-8 
0-8 


6- 4 
3'5 

7- 4 
1-9 


— 

1,173 
0-54 


18,000 

3,100 
407,000 




0-00122 


Lachrym. 

Suffoc. 

Lachrym 

" 


10 
5 

1-4 
7 


70 
20 
15 
50 


3,000 
450 
1,500 
7,000 


30,000 
5,OO0 

15,000 
3,500 


127 
36-j 

112 

12-5 

6l 


1-7 

0- 7 
r6 

1'2 

1- 9 


6-g 
o-g 
5-7 

2- 1 

3- 7 


10-3 
603 
16-9 
1,001 
89 


26,000 
873,000 
184,000 
3,300,000 
200,000 


0-00093 
0-0019 
o-oon 
0-0015 


Suffoc. 
Toxic 
Lach. Suf. 
Tox. Lach 
,» 


5 

I-I 
2 

5 


40 

50 
50 
85 


500 
1,000-4,000 
2,000 

2,000 


5,000 

2,000 
20,000 

4,000 
4,000 


208 


1*3 


6-0 




2,100 


0-00089 


Irritant 


3 


30 


3,000 


5,000 


2I7'5 


1-3 


5'4 


0-115 


625 


0-00088 


Vesicant 








1,500 


15,000 


333 


1-3 


— 


0-0005 


0-68 


0-0007 


Irritant 


o-i 


1 


4,000 


15,000 


257 


1-6 


7-7 




404 


0-0007 


,» 




16 




2,600 


105 


1-3 


4 




180,000 




Suffoc. 


14 


40 


500 


4,700 


154 


2-2 


7 




21,100 


00009 




20 


50 


400 


4,700 


156 
73-5 


1-7 
1-5 


6 
4 




20,000 


o-ooi I 


Suff. Ves 
Suffoc. 


1 


10 


3,000 


5,000 


377 


1-4 




0-0002 


0-16 




Irritant 


o-i 


025 


4,000 


10,000 


132 


1-8 


5-5 


8-5 


74,440 


0-OO102 


Suff. Ves. 


2 


25 


3,000 


5,600 



Column 17. Limit of Insupportability : the maximum concentration (in mgm. per cu. m.) which a normal man can 
support without injury for I minute at the most (Flury ; Vedder ; Lustig ; Lindemann ; Aksenov). 

Column 18. Mortality product : the product of the concentration of the substance in air (in mgm. per cu. m.) by the duration 
of its action (in minutes) to cause death (Flury ; Meyer). See p. 3- 

Column 19. These data are due to Prentiss, and in general refer to a time of exposure of 10 minutes. See p. 4 . 



339 



Table XV. List of War Gases Prepared or Studied 



Name 


Formula 


MUitary name 


M. Wt. 


M. Pt 

°C. 


French 


English 


American 


o-Nitrobenzyl bromide . 


C.H^NOsJCHjBr 








216 


46-47 


Bromobenzyl cyanide 


C,H 6 CHBrCN 


Camite 




CA 


196 


25 


Chloroacetophenone 


C.HjCOCHjCl 






CN 


154-5 


58 


Bromoacetophenone 


C,H 6 COCH,Br 








199 


50 


Bromopicrin . , 


CBr,NO, 








298 


IO-2 


Tetrachlorodinitroethane 


(CC1.NO,), 








257-8 


H2-I43 


Dibromoethyl sulphide . 


S(CH,CH,Br), 


Bromlost 






247-8 


31-34 


Diiodoethyl sulphide 


S(CH,CH 2 I), 








341-8 


62 


Chlorovinyl dichloroarsine 


ClCH=CHAsCl a 




Lewisite 


Mi 


207-3 


— 18-2 


Dichlorovinyl chloroarsine 


(ClCH=CH) 2 AsCl 








233-3 




Trichlorovinyl arsine 


(ClCH=CH) s As 








259-4 


21 


Bromovinyl 

dibromoarsine 


BrCH=CHAsBr 2 








340-6 




Chlorostyryl 

dichloroarsine 


C,H,CCl=CHAsCl, 








283-3 




Diphenyl bromoarsine . 


(C,H t ),AsBr 








3°9 


54-56 


Phenarsazine chloride 


NH(C,H 4 ),AsCl 




Adamsite 


DM 


277-4 


193-194 


Phenarsazine bromide . 


NH(C,H 4 ),AsBr 








321-8 




Phenarsazine cyanide 


NH(C 6 H 4 ) s AsCN 








272-0 


227 



340 



at the end of the War or immediately after the War 



B. Pt. 
°C. 


S.G. 


Vap. Tens. 

20° C. 
mm. Hg. 


Volatility 
mg./cu. m. 


242 


i-5 


0-012 


130 


245-47 


1-3 


0-013 


105 


260 








127/118 mm. 


2-8 






240 


2-05 




400 


190 


1-9 


o-394 


2,300 


230 


1-7 






260 


i-5 






("140-143/ 








1 16 mm. 








J 108-110/ 








[12 mm. 








54-56 








410 


i-6 


2 X io~" 













Principal 
biological 
action. 


Lower 
Limit 
Irritn. 


Limit of 
Insupporty. 


Lachrym. 






Lachrym. 


0-3 


3° 


Lachrym. 


0-3 


4-5 


Lachrym. 






Tox. lach. 


3° 




Tox. lach. 






Vesicant 






Vesicant 






Vesicant 


o-8 


48 


Vesicant 






Irritant 






Irritant 






Sternut. 


o-i 


0-4 









Mortality-product 



German data American data 



7.500 
4,000 



1,500 



3.500 
8,500 



30,000 



341 



AUTHOR INDEX 



Abeixi, 135 
Adams, 273, 277, 320 
Aeschlimann, 326 
Aksenov, 2, 180 
Alexander, 237, 245 
Alexejev, 103, 108, 258, 
262 

Alexejevsky, 132, 134, 
153. 17°. 171. J 73. i7 8 . 
265 

Alsterberg, 195 
Argo, 163 
Atkinson, 136 
Auger, 274 
Auwers. 120 
Autenrieth, 212 

Backer, 171, 278, 283 
Bader, 50 
Balard, 37 
Bales, 215, 237 
Bamberger, 135 
Barkenbus, 158 
Bart, 303 

Bartal, 57, 69, 74, 75 
Barthelemy, 105 
Baskerville, 66 
Bassett, 171 
Bausor, 217 

Baxter, 5, 6, 168, 192, 277 
Bayer, A., 52, 273, 277, 
328 

Bayer & Co., F., 136, 320 
Becker, 67 
Beckurts, 256 
Beek, 135 
Behrend, 267 
Behrens, 144 
Beilstein, 40, 132 
Bell, 217, 226, 236 
Bellinzoni, 314, 317 
Benedict, 42 
Benediktov, 319 
Bennett, 18, 216, 229, 236 
Berend, 52, 53 
Bergreen, 214 
Berlin, 283 
Bernhardi, 120 
Berthelot, D., 89, 101 
Berthelot, M., 47, 89 



Berthollet, 188 
Bertrand, 165 
Besson, 74, 260 
Bezzenberger, 5, 168, 277 
Biechler, 109 
Biesalsky, 52, 87 
Biltz, 52, 53, 163, 173 
Birckenbach, 58, 77, 78 
Bischof, 149, 186 
Black, J. H. 169, 179, 225 
Black, O. F., 326 
Blasi, 298 

Blicke, 299, 301, 302, 303, 

308, 311, 312 
Bly, 203 
Bodenstein, 66 
Boggio-Lera, 216, 232 
Bolas, 175 
Boord, 217 
Bougault, 328 
Boulin, 225, 258, 265 
Bozza, 221 
Bose, 71 
Brauner, 38 
Bredig, 185 
Brenneisen, 176 
Brinton, 333 
Brochet, 94 
Brunck, 54 
Buchanan, 185, 186 
Bunbury, 73 
Bunsen, 42, 273 
Burrows, 163, 166, 174, 

243, 244, 283 
Burton, 289, 301, 313, 

319. 320, 323, 325 
Buruiana, 247 
Bushong, 269 
Butlerov, 122 
BUscher, 284, 293 

Cahours, III 
Cannizzaro, 129, 130, 131, 

134, 190 
Carrara, 214, 259 
Carroll, 148 
Chapman, 64 
Chattaway, 190, 209 
Chauvenet, 72 
Cherniak, 175 



Chlopin, 37 

Chrzaszczevska, 128, 150, 

152, 159 
Chugaev, 29 
Chvalinsky, 95, 159 
Claesson, 261 
Claisen, 187 
Clarke, 218, 223, 239 
Clements, 158 
Clibbens, 155 
Cloez, 149, 190 
Coffey, 215 
Cohen, 66, 67 
Collet, 159 
Conant, 218, 289 
Conrad, 118 
Contardi, 72, 320, 321 
Cook, 194, 195, 274, 332 
Cossa, 168 
Cosslett, 187 
Councler, 115 
Craft, 155 
Cretcher, 92 
Cristaldi, 93 
Cristea, 271 
Crouzier, 191 

Dafert, 284 

Danaila, 166 

Dancer, 39 

Danneel, 259 

Das, 172, 177 

Das-Gupta, 278, 285 

Davies, 228, 233, 234, 

238, 239 
Davy, 59 

Dawson, 230, 233, 234 
Deckert, 176, 178, 208 
Dehn, 273, 279, 283, 301 
Delepine, 67, 86, 88, 89, 

124, 125, 223, 335 
De Paolini, 58 
Descud6, 93 
Desgrez, 231 
Despretz, 217, 218 
De Stackelberg, 134 
Dewar, 48, 49, 50 
Diels, 119 
Dollfus, 78, 79, 164 
Douris, 86 



34s 



AUTHOR INDEX 



343 



Dow Chemical Company, 
38 

Draeger, 56, 231 
Dubinin, 81, 114, 177, 180 
Dudek, 312 
Dufilho, 327 
Dumas, 71, 100, 102 
Dunant, 66 
Duppa, 1 19, 121 
Dyckerhof, 160 

Ehrlich, 24 
Eichler, 42 
Eldred, 186 
Elson, 324 

Emmerling, 57, 60, 74, 

152, 161 
Endres, 77 
Engel, 29, 32, 177 
Engelhardt, 73 
Engler, 161, 162 
Epbraim, 259 
Epstein, 286 
Ercoli, 72 

Erdmann, 61, 65, 75 
Erlenmeyer, 266 
En-era, 131 
Ewins, 330 

Fauconnier, 79 
Federal Laboratory, 160 
Felsing, 241 

Ferrarolo, 22, 194, 217, 
265, 271, 286 

Ferri, 2, 173, 199, 200, 242 

Fieldner, 176, 180 

Fischer, 323 

Fleury, 333, 

Florentin, 105, 108, no 

Fluerscheim, 133 

Flury, 3, 37, 74, 109, no, 
114, 121, 194, 223, 248, 
265, 269, 298, 302, 313, 

317 
Fordos, 207 
Fosse, 69 
Fox, 169 

Frankland, 170, 213 
Freundlich, 49 
Frickhinger, 104 
Friedel, 155 

Fries, 67, 122, 160, 173, 

223, 224, 272 
Frisch, 82 
Fritsch, 148, 149 
Froboese, 55 

Fromm, 236, 237, 241, 
245. 3°8 



Fuchs, 93. 95. i°8, 255, 
257. 258 

Ganassini, 41, 204 

Garden, 169 

Gastaldi, 205 

Gaudechon, 89 

Gautier, 55, 154, 158, 159 

Gavron, 277, 311 

Geisse, 170 

Gelis, 207 

Germann, 72 

Gershevich, 172 

Geuther, 143 

Gibson, 156, 218, 222, 
223, 228, 230, 235, 240, 
241, 277, 279, 282, 286, 
289, 293, 301, 308, 313, 
3i9, 320, 323, 324, 325 

Gilchrist, 242 

Giua, 148, 152, 223 

Glaser, 82 

Gloyns, 207 

Goddard, 303 

Gomberg, 222, 223, 226 

Gorsky, 324 

Goswami, 100 

Gotts, 78 

Graebe, 154, 155 

Grassi, 92, 93 

Green, 222, 284, 287, 288, 
291, 294, 295 

Gregor, 206 

Grice, 56 

Griffin, 284 

Griffith, 54. 5° 

Grignard, 62, 105, 107, 
no, 116, 191, 241, 245, 
248, 252, 307 

Grodsovsky, 144 

Groves, 174 

Gryszkiewicz, 273, 293, 
301, 308, 319, 325 

Guareschi, 206 

Guenter, 297 

Guignard, 205 

Guillemard, 179 

Guthrie, 35. 217. 218, 219, 
221, 222 

Gutmann, 193. r 95. 209 

Gutzeit, 326 

Guyot, 263, 267 

Haber, 3 

Hackmann, 21, 58, 147 
Haga, 143 
Hahn, 159 
Hamilton, 320 



Hanne, 45 

Hanslian, 44, 217, 223, 

243, 272, 320 
Hantzsch, 188 
Hanzlik, 174, 273, 279, 

284, 302, 313 
Harned, 173 
Harries, 143 
Hartel, 171 
Haussermann, 135 
Held, 188 

Helfrich, 212, 215, 229, 
237, 241, 245, 246 

Hennig, 178 

Henry, 97, 117, 119 

Hentschel, 99, 102, 104, 
105, in, 113, 123 

Herbst, 5, 7, 8, 9, in, 
173, 277, 282, 309, 316 

Hermsdorf, 183, 205 

Heumann, 269 

Heyden, 116 

Hieber, 50 

Hloch, 49 

Hoch, 174 

Hock, 50 

Hoffmann, 70, 166, 170 
Hofmann, 69, 74, 92, 271 
Hollely, 250 
Holmes, 101, 133 
Hood, in, 115 
Hoogeveen, 174 
Hoover, 56 

Hopkins, 225, 227, 250 
Hochst Fabr., 113 
Hunnius, 154, 162 
Hunt, 285 

Hunter, 163, 166, 175, 176 

Ingold, 45, 128, 130 
Ipatiev, 278, 300, 310 
Ireland, 172, 178 
Italien, 54 
Ivanov, 145 

Jackson, 223, 241, 252 
James, 163, 211, 213 
Jankovsky, 29 
Jastrzebsky, 155 
Jaxubovich, 172 
Jedlicka, 175 
Jobb, 240 
Jofinova, 205 
Johnson, 236, 240, 277, 

279, 286, 289, 319 
Jones, 48, 49 
Jonescu, 188 



344 



AUTHOR INDEX 



Jorg, 241 
Jurecev, 331, 334 

Kahn, 59 
Kalb, 319 
Kamm, 92 

Kappelmeyer, 307, 310, 

314. 3 2 3 
Kast, 53 

Katscher, 93. 95. !° 8 . 2 55. 

257. 258 
Katz, 56 

KekuM, 132, 134, 138, 166 
Kireev, 66 
Kiss, 173, 205 
Klason, 211, 213, 214 
Klebansky, 71 
Klemenc, 46, 189 
Klepl, 102 

Kling, 69, 74, 82, 83, 87, 

99, 105, 108, 110, 112 
Knoll, 197 
Kobert, 42 

Kolbe, 173, 174, 213, 214 
Kolobaiev, 81 
Kolthoff, 204 
Komissarov, 72, 261 
Korten, 156, 160 
K6chling, 269 
Kolliker, 87, 335 
Kraft, 103, 108, 258, 262 
Krauskopf , 80 
Krczil, 168, 177 
Kremann, 264 
Kretov, 81, 88, 89, 170, 

176, 200, 241, 243, 245, 

283, 292, 301 
Kuhlberg, 131 
Kumpf, 134, 135 

Labat, 179, 327 

Labriola, 145 

La Coste, 279, 298, 302, 

3i°. 3i4 
Lamb, 40, 56, 1 77 
Landolt, 39 
Langer, 47 
Laqueur, 74 
Lauth, 130 
Lawrie, 45, 50, 51 
Lawson, 230, 233, 234, 239 
Lebeau, 185 
Leitner, 11 
Lellmann, 160 
Lemoult, 50, 51 
Lenher, 57 
Le Pape, 140 
Levaillant, 255, 257, 258, 

260, 261, 263, 267, 268 



Levinstein, 223, 242 
Levy, 175 

Lewin, 144, 237, 244 

Lewis, 284, 285, 289, 290, 
291, 292, 293, 294, 295, 
308, 309, 319, 320, 332 

Libermann, 5, 133, 198, 
231, 289, 295. 3io.325 

Lieben, 134, 135 

Liebermann, 273 

Liebig, 206 

Lindemann, 135, 147, 176, 
214, 225, 230, 258, 284, 

317 
Linhard, 185 
Linnemann, 149, 150 
Lipmann, 121 
Litterscheid, 92, 94, 96 
Ljungreen, 54 
Ljutkina, 103, 262 
Lob, 131, 138 
Lobry de Bruyn, 144 
Loew, 22 

Lustig, 2, 271, 279, 284 
Luther, 5 



Macbeth, 172, 176 
Made, 182 
Madesani, 2, 173, 199, 200 
Maercker, 132 
Magnus, 74 
Mai, 188 
Malachovsky, 58 
Malinovsky, 301, 312 
Mameli, 60 
Mamoli, 221 

Mann, 229, 232, 233, 235, 

284, 291, 294, 296 
Mannich, 159, 162 
Mark, 197 
Marsh, 54 
Marshall, 229 
Maselli, 92 
Matheson, 159, 162 
Matuszak, 71, 86, 87 
Mauguin, 189, 208 
Mauritz, 162 
Maxim, 250 
Mayer, 176, 244 
Mazza, 170 
Mazzucchelli, 62, 67 
McCombie, 237, 245 
McGrath, 283 
McKee, 260 

McKenzie, 315, 316, 317 
Melnikov, 67, 72, 112, 113, 
116, 170, 172, 176 



Meyer, E., 195 

Meyer, J., 4, 13. 23. 67, 74, 
104, 119, 223, 231, 255, 
259, 266, 310, 317 

Meyer, V., 134, 175, 218, 
220, 221, 222, 223, 236 

Mez, 82 

Michael, 128 

Michaelis, 35', 297, 298, 
300, 302, 304, 305, 306, 

310. 3 12 , 314 
Michler, 70 
Mieg, 273, 283, 312 
Miller, 293 
Mills, 166 
Mitic, 70, 112 
Mittasch, 48, 49, 50, 56 
Moissan, 187 
Mond, 47 
Monnot, 89 
Montgomery, 67 
Mooney, 193 
Moreschi, 91 

Morgan, 303, 304, 305, 

3°6, 3 12 , 315 
Moureu, 128, 140, 141, 

142. 143 
Mohlau, 159, 161, 162 
Mulder, 149 

Mumford, 5, 6, 224, 233 

Muntsch, 231 

Murdoch, in, 115 

Miiller, E., 232 

Muller, H., 119 

Miiller, M., 143, 268 

Muller, U., 37, 96, 97, 114, 
121, 122, 135, 138, 144, 
160, 161, 194, 199, 200, 
242, 243, 268, 269, 272, 
279, 284, 293, 318, 325, 
326 

Myers, 219 



Nametkin, 278, 283, 290, 

292, 328 
Naumann, 120, 189 
Nef, 53, 58, 76, 104, 122, 

144, 149, 189, 201, 203 
Nekrassov, 21, 24, 50, 72, 

112, 114, 116, 128, 141, 

149, 155. 171. J 72. 175. 
178, 194, 196, 201, 240, 
261, 271, 278, 280, 283, 
286, 289, 290, 292, 328 
Nenitzescu, 88, 222, 240, 
244, 245, 274, 303, 315, 
3 J 9 



AUTHOR INDEX 



345 



Nesmejanov, 59 
Nessler, 83 
Nickelson, 237 
Nicloux, 55 
Nielsen, 12, 73 
Niemann, 218 
Nierenstein, 144, 155 
Nieuwland, 52 
Noelting, 131 
Norris, 93. 97. *37. 151. 
306, 315. 316 

Oberhauser, 193, 209 
Oberfell, 176 
Obermiller, 249 
Odeen, 225, 241 
Offerhaus, 43 
Olsen, 82, 84 
Orton, 167 
Ostwald, 5 
Ott, 58 
Otto, 256 
Oxford, 228, 238 

Page, 207 
Pana, 88 

Pancenko, 82, 125, 159, 

178, 194, 312 
Panting, 182 
Pascal, 223 

Paternd, 60, 62, 67, 73 
Perkin, 119, 121, 130 
Perkins, 35, 284, 289, 290, 

293. 294. 332 

Perret, 69, 103, 108, 109, 
no, in, 116 

Perrot, 69 

Pertusi, 205 

Peters, 227 

Petrov, 169 

Pfeiffer, 38 

Philips, 233, 304 

Phillips, 234 

Pinkus, 149 

Pittenger, 92 

Piutti, 165, 170 

Plaut, 66 

Plucker, 73, 114 

Poggi, 217- 

Ponomarev, 192 

Pope, 167, 215, 218, 222, 
223, 228, 229, 230, 232, 
233. 235. 241, 284, 291, 

294, 295, 296, 303, 304, 
305, 306, 309 

Popescu, 61 
Popiel, 128 
Posner, 146 



Postovsky, 80 
Power, 302, 303 
Prandtl, 58, 77, 78, 79, 
164 

Pratt, 172, 176 

Prentiss, 4, 37, 74, 114, 
138, 161, 173, 194, 242, 
258, 269, 279, 284, 289, 
293. 3°2. 313. 318, 326 

Price, 286, 287, 291, 294, 
295 

Przychocki, 242 
Puschin, 70, 112 

Quick, 273 

Rabcewicz, 95 
Radulescu, 167 
Radziszevsky, 136, 186 
Raiziss, 277, 300, 311 
Ramsperger, 105, in 
Raschig, 170 

Rasuvajev, 311, 319, 323, 
324 

Rathke, 171, 211, 212, 

213, 214 
Ray, 148, 155, 172, 177, 

178 

Redlinger, 250 
Redtenbacher, 140 
Reese, 298, 303 
Regnault, 5, 92, 189 
Reid, 215, 229, 237, 239, 

241, 243, 244 
Reimer, 196 
Renshaw, 286 
Renwanz, 231, 242 
Reymenant, 154 
Rheinheimer, 320, 325, 326 
Riche, 148, 217 
Rieche, 265 
Rimarsky, 190 
Rivat, no, 245, 248, 252, 

307 

Robertson, 330 

Rocciu, 148, 152 

Roeder, 298 

Rogers, 331 

Rohde, 146 

Rollefson, 67 

Romijin, 124 

Rona, 12, 97, 122, 133, 

135. 138. i69, 227, 243, 

310 
Rose, 206 
Rosen, 216 
R6se, 103, 171 
Ruedel, 176 



Ruff, 57, 164 
Rusberg, 270 
Rutz, 164 



Salzmann, 120 
Sammelt, 131 
Sanger, 326 
Sanna, 166 
Sarkar, 100 

Scarlatescu, 240, 244, 245 
Schatchard, 248, 252 
Scheele, 33, 181 
Scherlin, 286 
Schiff, 42 
Schmidt, F., 164 
Schmidt, H., 303 
Schmidt, J., 47 
Schmutz, 69, 82, 83, 87 
Scholl, 76, 156, 160, 176, 
191 

Schormiiller, 193, 209 
Schramm, 132, 136, 255, 
266 

Schroter, 225, 246, 248, 
249 

Schulze, 138, 259 
Schumacher, 57, 75 
Schiittzenberger, 62 
Schwen, 273, 311, 312, 

314. 3i5 
Secareanu, 167, 169 
Seide, 324 
Seil, 207 
Selinski, 120 
Sell, 120, 121, 201 
Selle, 53 

Sennewald, 58, 77, 78, 164 
Sergeev, 325 

Serullas, 189, 190, 191, 

193. 194 
Seubert, 194, 195 
Shimidzu, 194 
Shiver, 290 
Short, 132 

Sieverts, 183, 205, 334, 
335 

Simon, 189, 208, 225, 257, 

258, 263, 265, 267 
Skrabal, 101 
Slator, 122 
Slotta, 183, 191 
Slunesko, 58 
Smith, 125 
Smith, F. D., 303 
Smith, G. B. L., 148 
Smolczyk, 40, 41, 187, 205 
Soare, 166 



346 



AUTHOR INDEX 



Sobieransky, 150, 152 

Sokolovsky, 152 

Sonay, 94, 96 

Speyer, 49 

Spica, 246, 247 

Sporzynsky, 298 

Ssytschev, 171 

Staedel, 154. 157. 158. *59 

Stampe, 56, 249 

Staudinger, 59, 68, 79, 80 

Steinkopf, 193, 196, 197, 
215, 219, 229, 243, 255, 
260, 273, 283, 297, 299, 
308, 309, 3". 312. 314. 
315. 316 

Stenhouse, 165, 166, 170, 
174, 176, 179 

Stephen, 93, 96, 132, 219 

Stiegler, 285, 292, 295 

Stolid, 80 

Stolzenberg, 102, 105 
Storm, 41 
Straus, 45, 94 
Strughold, 284 
Studinger, 82 
Sturniolo, 314, 316, 317 
Suchier, 81 
Suszko, 155 

Tafel, 159, 162 
Tanner, 323 
Teichmann, 185 
Themme, 225 
Thiel, 94 
Thimme, 96 
Thomann, 73, 82 
Thompson, 169, 179. 225 
Thorpe, 136 
Tiemann, 122 



Timmermann, 264 
Tiscenko, 92, 96, 100 
Trochimovsky, 273 
Tronov, 172 
Trumbull, 167 
Turner, 283, 285, 3°3. 
304, 305, 306, 309, 319 

Uehlinger, 274, 332 
Uhl, 328, 332 
Ulich, 80 

Ullmann, 263, 265 
Ungar, 236, 237, 245 

Valdo, 92 

Van der Laan, 133, 139 
Van der Sleen, 144 
Vandervelde, 118 
Vaughn, 52 

Vedder, 13, 223, 224, 290, 
293 

Vedekind, 135 
Ville, 86 

Vining, 303, 304, 305, 

308, 312, 315 
Vinokurov (Winokurow), 

"3 

Vies, 67, 69, 84, 103, 104 
Volhard, 100 
Von Braun, 196 
Vorlaender, 72 

Waddington, 105 
Wadmore, 190 
Wagner, 152 
Wald, 197 
Walker, 186, 227 
Waller, 205 
Walton, 308 



Ward, 154, 161 
Ware, 286 
Weber, 305 
Weddige, 100, 103 
Weidner, 232, 233, 242 
Wernlund, 224 
West, 67, 272 
Weston, 138, 269 
Wicke, 43 

Wieland, 76, 223, 280, 
284, 289, 292, 293, 295, 
320, 325, 326 

Wilkendorf, 164 

Wilkinson, 224 

Willcox, 269, 273 

Williams, 229 

Wilm, 104, 117, 268 

Wilson, 192, 225, 227, 228 

Winkelmann, 5 

Winkler, 35, 54 

Winokurow, 113 

Winterstein, 335 

Wirth, 4, 74, 231 

Wischin, 104 

Wispek, 136 

Witt, 24 

Wolff, 176 

Wood, 315 

Wurtz, 189 

Yablich, 233, 247, 249 
Yant, 84, 85 

Zappi, 141, 145, 188, 190, 

195. 273, 278 
Zernik, 226, 242, 248, 313 
Zierold, 201 
Zitovic, 29 
Zoppellari, 259 



SUBJECT INDEX 



Acetamide, a chloro, 118 
Acetate derivatives, ethyl, 117 
Acetic thioanhydride, chloro, 216 
Acetone, bromo, 13, 16, 150, 191, 194,268 
manufacture, 151 
preparation, isoj 
properties, 152 
chloro, 13, 16, 148, 260 
preparation, 148 
properties, 148 
tribromo, 149 
cyanohydrin, a chloro, 149 
fluoro, 148 
iodo, 13 

pentachloro, 149 
Acetones, dichloro, 22- 260 
Acetonyl sulphide, di, 149 
Acetophenone, a amino, 159 

a bromo, 161 

bromo trinitro, 162 

a chloro, 2, 3, 4, 8, 10, 155 
manufacture, 156 
preparation, 156 
properties, 157 

m nitro a chloro, 158 

aa dichloro, 158 

trichloro, 155, 159 

fluoro, 155 

a iodo, 159 

oxime, a chloro, 160 
Acetylene, dibromo, 22, 45, 50 

derivatives, 22, 45 

diiodo, 22, 45, 52 
Acrolein, 13, 22, 140 

chloro, 140 
Acrylic aldehyde. See Acrolein. 
Acyl halides as war gases, 57 
Adamsite. See Phenarsazine chloride. 
Adsorption of carbonyls on alumina, 50 

of war gases on carbon, 44, 50, 73 
on silica gel, 327 fn., 331 
Aerosols, 297, 313, 327 fn. 
Alcohol, chloromethyl, 91 
Aldehyde, chlorocrotonic, 140 

crotonic, 140, 149 

glycollic, 144 

propionic, 22 
Aldehydes as war gases, 140 
Alexejevsky's test for chloropicrin, 178 
Alkyl arsenates, 172 

phenarsazines, 326 

sulphates, 254 

disulphides, 172 

sulphides as war gases, 214 

sulphuric acids, 254 
Allied method for manufacturing 

mustard gas, 221 



Alumina, adsorption of iron carbonyl 
by, 50 

American method for manufacturing 
ethyl dichloroarsine, 281 
phenarsazine chloride, 321 
Amine, methyl, 170, 186 

triphenarsazine, 324 
Amino acetone, 149 

acetophenone, a, 159 
Ammonia as solvent for carbon 
monoxide, 44 

test for cyanogen bromide, 209 
iso-Amyl dichloroarsine, 273 
Analysis of war gases, 40, 53, 81, 98, 

123, 138, 144, 176, 204, 246, 269, 326 
Aniline, trichloro, 260 

phenacyl, 159 

test for chlorine, 41 

for phosgene, 69, 82, 83, 84 
Antigas niters, 44, 50, 68, 73 
Antimony as absorbent for chlorine, 

88 

Apparatus for carbon monoxide 
determination, Draeger's, 56 
for chloropicrin, Engel's indicator, 
177 

Aquinite (chloropicrin, g.v.), Table 
XIV. 

Aromatic esters as war gases, 127 
Arsane, phenylthio, 240 
Arsanthrene chloride, 319 
Arsenamide, diphenyl, 310 
Arsenates, alkyl, 172 
Arsenic acid, /} chlorovinyl, 286, 291, 
292 

dichlorovinyl, 294 
ethyl, 283 

hydrochloride, diphenyl, 311 
methyl, 278 

nitrate, dichlorovinyl, 294 

diphenyl, 311 
phenyl, 300 

diphenyl, 310, 311, 313, 317 
sulphate, diphenyl, 311 
anhydride, tetraphenyl tetrachloro, 
317 

atom in war gases : effect on 

properties, 18, 271 
trichloride, determination in phenyl 

dichloroarsine, 335 
compounds as war gases, 271 
oxide, trichlorovinyl, 296 
Arsenfmide, methyl, 278 

phenyl, 300 
Arsenious oxide, dichlorodivinyl, 294 
ethyl, 283 
methyl, 277 



347 



348 



SUBJECT INDEX 



Arsenious oxide, phenyl, 299, 300 
(dimer), 299 
diphenyl, 310, 317 
sulphide, dichlorovinyl, 295 
methyl, 278 
phenyl, 301 
diphenyl, 311, 312 
thiocyanate, diphenyl, 312 
Arsenite, alkali phenyl, 300 

test for cyanogen iodide, sodium, 209 
Arsenobenzene, 302 
Arsilimine group, 296 
Arsine, 15, 271 

iso-amyl dichloro, 273 
anilino chloro phenyl, 300 
bromide, chloro diphenyl, 310 
perbromide, chloro diphenyl, 311 
bromo dichloro diphenyl, 314 
dimethyl, 273 
diphenyl, 314 
dibromo j8 bromovinyl, 285 
trichlorovinyl, 296 
ethyl, 273, 284 
tribromo diphenyl, 314 
pentabromo diphenyl, 314 
» butyl dichloro, 273 
chloro 0 chlorovinyl methyl, 278, 285 
phenyl, 286 
j8j8' dichlorovinyl, 19, 285, 287, 
293 

methyl naphthyl, 298 
dimethyl, 273 

diphenyl, 2, 3, 4, 6, 7, 17, 19, 20, 
302, 326, 333 

analysis, 326, 333 

manufacture, 304 

preparation, 302 

properties, 308 
diphenylamine. See Phenarsazine 

chloride, 
ditolyl, 20 
dichloro j3 chloroethyl, 22, 286 
chlorostyryl, 285 

P chlorovinyl, 6, 19, 22, 285, 289, 

329. 33 2 

analysis, 326, 329, 332 

manufacture, 288 

preparation, 286 

properties, 289 
ethyl, 2, 3, 4, 272, 279, 329 

analysis, 326, 329 

manufacture, 281 

preparation, 280 

properties, 282 
methyl, 6, 7, 20, 273, 329, 332 

analysis, 326, 329, 332 

manufacture, 275 

preparation, 274 

properties, 276 
phenyl, 19, 20, 298, 326, 333 

analysis, 326, 333 

preparation, 298 

properties, 299 
j8j8' dichlorovinyl cyano, 295 

methyl, 279 
trichloro diphenyl, 310 



Arsine, j8|8'|8" trichlorovinyl, 19, 285, 
286, 287, 295 
tetrachloro methyl, 277 
cyano diphenyl, 7, 20, 314, 334 
analysis, 326, 334 
manufacture, 316 
preparation, 315 
properties, 316 
dicyano methyl, 273 

phenyl, 301 
fluoro methyl naphthyl, 298 

dimethyl, 273 
iodo diphenyl, 311, 312 
diiodo j8 chlorovinyl, 292 

ethyl, 283 
triphenyl, 19, 303, 304, 305 
diAtsine, tetraphenyl, 312 
Arsines, aliphatic, 272 et seq. 
aromatic, 297 et seq. 
heterocyclic, 318 et seq. 
Arsonium triiodide, dimethyl diphenyl, 
312, 317 

nitrate, trichloro hydroxy trivinyl, 296 
Aryl phenarsazines, 326 
A Staff (chloroacetone). See Table XIV. 
Atmospheric agencies and war gases, 12 
Auxotox groups, 25 

BA (bromoacetone). See Table XIV. 
Bayer's plant for the manufacture of 

the chloroformate war gases, 106 
Beils tern's test for halogens, 40 
Benzaldehyde (dimethyl amino-) — 

diphenylamine test for phosgene, 81 
Benzene, chloro, use mixed with 

mustard gas, 10 
Benzidine acetate test for detection of 

hydrocyanic acid, 205 
Benzoate, chloromethyl, 109 
Benzoic acid, dibromo amino, 133 
Benzophenone, 114 
Benzoyl cyanide, 187 
Benzyl amine, tri, 134 

bromide, 7, 13, 16, 17, 21, 132, 138, 
139. 196 
analysis, 138, 139 
manufacture, 133 
preparation, 132 
properties, 133 
p bromo, 131 
chloride, 21, 129 
analysis, 138, 139 
manufacture, 129 
preparation, 129 
properties, 130 
p bromo, 131 
cyanide, 131 

bromo, 6, 11, 22, 196 
fluoride, 128 
iodide, 13, 16, 134 
analysis, 139 
preparation, 134 
properties, 134 
sulphide, 132 
Bertholite (chlorine, q.v.). See Table 
XIV. 



SUBJECT INDEX 



349 



Bibi (dibromomethyl ether, q.v.). See 

Table XIV. 
Biological classification of war gases, 28 

properties of war gases, 1, 15 et seq., 
23, 28 
Black powder, 46 

Bleaching powder, 36, 231, 242, 284 
Blondes, effect of mustard gas on, 242 
Blue Cross gases, 28 
Bn Stoff (bromomethyl ethyl ketone, 

q.v.). See Table XIV. 
Boiling point of war gases, 8, 9 
Bougault's test for arsenic compounds, 

328 

Boyle-Gay Lussac law, 33 fn. 
Bromide, />-bromobenzyl, 131 

dichloro ethyl sulphide, di-, 230 
tetra-, 230 

cyanogen, 6, 8, 22, 187, 191 
analysis, 209 
manufacture, 191 
preparation, 191 
properties, 192 

cyanuryl, 192 

0 nitro benzyl, 128 

oxalyl, 59 

phenarsazine, 319 

xylyl, 13, 14, 136 

xylylene, 136 
Bromine, 37, 42, 43 

analysis, 42, 43 

hydrate, 39 

manufacture, 38 

preparation, 37 

properties, 38 
Bromlost (dibromoethyl sulphide, 

q.v.). See Table XV. 
Bromoacetate, ethyl, 119 
Bromoacetone, 13, 16, 150, 191, 194, 268 

manufacture, 151 

preparation, 150 

properties, 152 
Bromoacetophenone, 161 
p Bromobenzyl bromide, 131 

chloride, 131 

cyanide, 6, 11, 22, 196 
Bromoethyl chlorosulphonate, 255 

methyl ketones, 25 
Bromomethyl ethyl ketone, 153 
Bromophosgene. See Carbonyl 

bromide. 
Bromopicrin, 174 
Bromotoluene, 17 
Bromo trinitro acetophenone, 162 
jS Bromovinyl dibromoarsine, 285 
diBromoacetylene, 22, 45, 50 
diBromo trichloro vinyl arsine, 296 

ethyl sulphide, 16, 18, 215, 243 
sulphone, 244 
sulphoxide, 244 

formoxime, 21, 58 

iodoethylene, 51 

methyl ether, 91, 96 
triBromo amino benzoic acid, 133 

nitromethane, 174 

aj8 dinitroethane, aaj8, 163 



tetraBromo ethylene, 51 

diphenylamine, 324 
pentaBromo diphenyl arsine, 314 
Brunettes, effect of mustard gas on, 242 
B Stoff (bromoacetone, q.v.). See 

Table XIV. 
Building materials, penetration by 

mustard gas, 225 
n Butyl dichloroarsine, 273 

CA (bromobenzyl cyanide, q.v.). See 

Table XV. 
Cacodyl, phenyl, 313 
Calcium hypochlorite, 36 

for decontamination of mustard 
gas, 231, 242 
of dichloro ethyl arsine, 284 
phenyl dithiocarbamate, 201 
Camite (bromobenzyl cyanide, q.v.). 

See Table XV. 
Campiellite, 194 
Candles, irritant, 160, 297 
Carbon, activated, 44, 73, 1 14, 173, 180, 
317 

atom in war gases, divalent, 44 
dioxide in air, determination in 

presence of chlorine, 43 
monoxide, 44, 45, 53. 55 
analysis, 53. 55 
manufacture, 46, 62 
preparation, 46 
properties, 46 
tetrachloride, use mixed with 

mustard gas, 10 
tetraiodide, 171 
Carbonate, dichloroethyl, 114 
hexachloromethyl, 102, 115 
tetraethyl ortho-, 171 
ethylene glycol, 71 
glycerol, 72 
methyl 71 
phenyl, 113 

trichloromethyl, 113 
Carbonyl bromide, 57, 59. 74, 175 
preparation, 75 
properties, 75 
chloride, 2, 6, 8, 11, 12, 27, 57, 59 
analysis, 81 et seq. 
manufacture, 62 
preparation, 60 
properties, 65 
chlorobromide, 69 
cyanide, 57, 58 
fluoride, 57 
group in war gases, 23 
iodide, 59 
iron penta-, 44, 47 

nona-, 49 
nickel tetra-, 44, 49 
Carbonyls, metal, 44, 47, 49 
CDA (diphenyl cyano arsine, q.v.). See 

Table XIV. 
CG (carbonyl chloride, q.v.). See 

Table XIV. 
Cedenite (0 and ^-nitrobenzyl chloride) , 
135 



35° 



SUBJECT INDEX 



Cellulose acetate, 101, 185 

Chemical classification of war gases, 29 
properties of war gases, 1, 12 
Warfare Service (U.S.A.), 247, 223 
fn. 1 

Chemlsch-TechnischenReichsanstalt, 86 
Chloramine-T, 232, 295. 296, 313, 325 
Chloride, p bromobenzyl, 131 

p chlorobenzyl, 131 

dichloroethyl sulphide di-, 230, 231, 
234 

cuprous, compound with mustard 

gas, 241, 251 
cyanoformyl, 58 
cyanogen, 6, 188 
cyanuryl, 189, 223 
of lime. See Calcium hypochlorite, 
metal, compounds with dichloroethyl 

sulphide, 241 
0 nitrobenzyl, 21, 135 
oxalyl, 59, 79 

phenarsazine, 301, 318, 319, 320, 
329, 335 
analysis, 329, 335 
manufacture, 321 
preparation, 320 
properties, 322, 323 
phenoxarsine, 319 
phenyl carbylamine, 200 
manufacture, 202 
preparation, 201 
properties, 203 
platinum, 47, 241 
sulphuryl, 258, 269, 270 
analysis, 269, 270 
preparation, 259 
properties, 259 
tin, 241 

titanium, 187, 241 
zinc, 187 

Chlorinated methyl chloroformates, 104 
Chlorine, 8, 10, 33, 40, 42, 88 

analysis, 40, 42, 88 

properties, 33 

water, 35, 41 
a Chloroacetamide, 118 
Chloroacetate, ethyl, 117 
Chloroacetic thioanhydride, 216 
Chloroacetone, 13, 16, 148, 260 

cyanohydrin, 149 
a Chloroacetophenone, 2, 3, 4, 8, 10, 
154. 155 

manufacture, 156 

preparation, 156 

properties, 157 

oxime, 160 
n Chloroacetyl urethane, 119 
Chloroacrolein, 140 
Chlorobenzene, 10, 260 
p Chlorobenzyl chloride, 131 

cyanide, 22, 181 
Chlorobromophosgene, 69 
Chlorotribromoacetone, 149 
Chlorocarbonate, methyl, 99 
Chlorocrotonic aldehyde, 140 
jS Chloroethane sulphonic acid, 230 



/J Chloroethyl dichloroarsine, 22, 286 

chloroformate, 72 
Chloroethyl chlorosulphonate, 255, 260 

diurethane, 186 

vinyl sulphide, 238 
Chloroformates, 99 et seq. 

/} chlorethyl, 72 

chlorinated methyl, 104 
analysis, 123 et seq. 
manufacture, 104, 106 
preparation, 105 
properties, 107 

(mono)chloromethyl, 8, 107 

dichloromethyl, 109 

trichloromethyl, 2, 3, 4, 7, 10, 14, 110 

methyl, 101 

isopropenyl, 71 
Chloroformoxime, mono, 76 

di, 77, 165 
a Chlorohydrin carbonate, 72 
10 Chloro 5:10 dihydro phenarsazine, 

301, 318, 319, 320, 329, 335 
Chloromethyl alcohol, 91 

benzoate, 109 

chloroformates, 104 

chlorosulphonate, 258 
a Chloromethyl ethyl ketone, 17 
/J Chloromethyl ethyl ketone, 17 

sulphide, 215 
Chloropicrin, 2, 3, 4, 6, 7, 8, 10, 11, 13, 
14, 165 

analysis, 176, 179 

manufacture, 166 

preparation, 166 

properties, 167 
p Chloropropionic nitrile, 239 
/S Chlorostyryl dichloroarsine, 285 
Chlorosulphonate, bromoethyl, 255 

chloroethyl, 255, 260 

chloromethyl, 258 

ethyl, 268 

methyl, 258, 262, 266 

propyl, 255 
Chlorosulphonic acid, 93, 255, 269, 270 
/} Chlorovinyl arsenic acid, 286, 291 , 292 

arsenious oxide, 290, 291 
sulphide, 292 
Chlorovinyl arsines, 284 et seq. 
fi Chlorovinyl dichloroarsine, 6, 11, 19, 

22, 28, 285, 289, 329, 332 
a Chlorovinyl /J chloroethyl sulphide, 

234 

/3 Chlorovinyl /} chloroethyl sulphide, 
234 

diiodoarsine, 292 

methyl chloroarsine, 278, 285 
diChloroacetones, 22, 260 
aa diChloroacetophenone, 158 
diChloro bromovinyl arsine, 291 
j8j3' diChlorobutyl sulphide, 215 
88' diChlorobutyl sulphide, 216 
diChloro bromo diphenyl arsine, 314 
<xj8 dichloroethyl vinyl sulphide, 237 
j8j8' dichloroethyl carbonate, 114 

ether, 18, 92 
dichloroethyl selenide, 217 



SUBJECT INDEX 



35i 



j8j8' diChloroethyl sulphate, 261 
aoc' diChloroethyl sulphide, 25, 215 
j8j8' diChloroethyl sulphide, 6, 7, 8, 10, 
11, 12, 13, 16, 17, 18, 25,26,27, 
28, 217, 246, 249, 250 
analysis, 246, 249, 250 
dibromide, 230 
tetrabromide, 230 
dichloride, 230, 231, 234 
trichloroiodide, 232 
pentachloroiodide, 232 
manufacture, 220 et seq. 
preparation, 217, 219 
properties (physical), 223 
(chemical), 226 
disulphide, 18 
sulphone, 228, 229, 233 
sulphoxide, 228, 229, 231, 234 
telluride, 217 
diChloroformoxime, 21, 58, 77, 165 
preparation, 77 
properties, 78 
diChloromethyl chloroformate, 104, 
109, 123 
ether, 2, 3, 4, 13, 92, 98 
analysis, 98 
manufacture, 93 
preparation, 93 
properties, 94 
oc'jS diChloromethyl ethyl ketone, 147 
diChloromethyl sulphate, 95. 255. 2 57 
diChloronitro ethane, sodium salt, 172 
diChlorodinitromethaae, 78 
diChlorotetranitro ethane, 163 
|8j8' diChloropropyl sulphide, 215 
yy' diChloropropyl sulphide, 216 
j8j8' diChlorovinyl arsenic acid, 294 
nitrate, 294 
arsenious oxide, 294 

diChlorovinyl diarsine 
sulphide, 295 
$3' diChlorovinyl chloroarsine, 19, 285, 
293 

analysis, 326, 328, 331 

manufacture, 288 

preparation, 286 

properties, 288, 289, 290 
cyanoarsine, 295 
methyl arsine, 279 
triChloro acetophenones, 155, 159 

aniline, 260 
<xj3|8' triChloroethyl sulphide, 216, 233, 
234, 236 

triChloromethyl chloroformate, 2, 3, 4, 
6, 7, rp, 11, 104, 110 
analysis, 123, 125 
manufacture, 106 
preparation, 105 
properties, no 
JV diphenyl urethane, 113 
sulphonic chloride, 212 
ether, 95 
triChloronitro methane. See 

Chloropicrin. 
triChlorodinitro ethyl alcohol, 
potassium salt, 174 



triChloronitroso methane, 77, 164 
jSjS'jS" triChlorovinyl arsenoxide, 296 

arsine, 19, 284, 286, 288, 295 

hydroxy arsonium nitrate, 296 
PP'j}"P'" tetraChlorovinyl arsine 

sulphide, 295 
ajSjSjS' tetraChloroethyl sulphide, 233 
aa'pp' tetraChloroethyl sulphide, 237 

sulphoxide, 232 
tetraChloromethyl ether, 95 
tetraChloro nitroethane, 21 

dinitro ethane, 21, 163, 164, 173 
preparation, 173 
properties, 174 

propyl sulphide, 216 
pentaChloro acetone, 149 
aaa'jSjS' pentaChloro ethyl sulphide, 235 
pentaChloro methyl ether, 95 
hexaChloro ethane, 53 
aaa'jSjS'jS' hexaChloro ethyl sulphide, 

233, 235 

hexaChloro methyl carbonate, 102, 115 
ether, 95 

aaa'/SjS/S'jS' heptaChloro ethyl sulphide, 
235 

Chronological classification of the war 

gases, 32, Table XIV. 
Chugaev s classification of the war 

gases, 29 

Qcl (diChloromethyl ether, q.v.). See 

Table XIV. 
Clairsite (perchloromethyl mercaptan, 

q.v.). See Table XIV. 
Clark I. (diphenyl chloroarsine, q.v.). 

See Table XIV. 
Clark II. (diphenyl cyano arsine, q.v.). 

See Table XIV. 
Classification of the War Gases, 
Chapter III. 
biological, 28 
chemical, 29 

chronological, 32, Table XIV. 

Engel's, 32 

Jankovsky's, 29 

military, 27 

physical, 27 

physiopathological, 28 

tactical, 27 
CN (chloroacetophenone, q.v.), 156, 

Table XV. 
Collongite (phosgene, q.v.). See Table 
XIV. 

Concentration of war gases in air, 37, 183 
Congo Red test paper for detecting 

dichloroethyl sulphide, 246 
Contardi's method for manufacturing 

phenarsazine chloride, 321 
Corrosion of containers by war gases, 1 4 
Cross gases, blue, 28 
green, 28 
white, 28 
yellow, 28 
Crotonic aldehyde, 140, 149 
Cryptogram destruction by 

chloropicrin, 165 
Crystal violet, 113 



352 



SUBJECT INDEX 



C Stoff (methyl chlorosulphonate, 

q.v.), 266, Table XIV. 
Cuprous chloride addition compounds 
with dichloroethyl sulphide, 241, 251 
Cyanamide, 190, 193 
isoCyanate, phenyl, 203 
Cyanic acid, 190, 193 
Cyanide, benzoyl, 187 

bromobenzyl, 6, 11, 14, 22, 196 
manufacture, 197 
preparation, 196 
properties, 198 
chlorobenzyl, 22, 181 
phenarsazine, 181, 319, 325 
group in war gases, 21 
Cyanoacetate, ethyl, 1 19 
Cyano amino chloroformoxime, 78 
benzyl mercaptan, 200 
thiocyanate, 200 
thiosulphate, sodium, 199 
formate, methyl, 103 
formyl chloride, 58 
diCyano benzyl sulphide, 199 

stilbene, 199 
Cyanogen, para, 188 

bromide, 6, 8, 22, 187, 191 
analysis, 209 
manufacture, 191 
preparation, 191 
properties, 192 
chloride, 6, 186, 188, 208 
analysis, 208 
manufacture, 189 
preparation, 188 
properties, 189 
compounds, Chapter XIII. 
fluoride, 181, 187 
iodide, 22, 194, 209 
analysis, 209 
preparation, 194 
properties, 195 
Cyanuryl bromide, 192 
chloride, 186, 189 



DA (diphenyl chloroarsine, q.v.). See 

Table XIV. 
Decker t's apparatus for analysis of 

hydrocyanic acid in air, 208 
Decontamination, 13, 36, 73, 153, 154, 

231, 232, 233, 242, 284 
Delay in physiopathological action of 

war gases, 242 
Delepine's method of analysing the 

chloroformates, 125 
Delepine, Douris and Ville's method of 

analysing phosgene, 86 
Dick (ethyl dichloroarsine, q.v.). See 
Table XIV. 

methyl- (methyl dichloroarsine, 
q.v.) See Table XIV. 
Diphenylamine, tetrabromo, 324 

chloroarsine. See Phenarsazine 
Chloride. 
Diphosgene. See Trichloromethyl 

Chloroformate. 



Disacryl, 143 
Dithiane, 226, 236 

methiodide, 240, 244, 245 
Dithiophosgene, 214 
Divalent carbon atom in war gases, 44 
DM (phenarsazine chloride, q.v.). See 

Table XV. 
Draeger-CO-Messer apparatus for 

analysing carbon monoxide, 56 
D Stoff (dimethyl sulphate, q.v.). See 

Table XIV. 
Dubinin's method of analysis of 

chloropicrin, 180 
Dumas 's method of analysis of 

chloropicrin, 179 
Dynamite, 46 



ED (ethyl dichloroarsine, q.v.). See 

Table XIV. 
Ehrlich-Nekrassov theory, 24 
Engel's classification of the war gases, 
32 

indicator apparatus for analysis of 
chloropicrin, 177 
Ester, orthonitro trithioformic, 172 
Esters, halogenated, as war gases, 99 
E Stoff (cyanogen bromide, q.v.). See 

Table XIV. 
Ethane, amp tribromo <x(3 dinitro, 163 

dichloro tetranitro, 163 

trichloronitro, 21 

tetrachloro dinitro, 21, 163, 164, 
173 

hexachloro, 53 
tetranitro (salts), 174, 176 
Ether, benzyl ethyl, 130 
dibromomethyl, 91, 92, 96 

manufacture, 97 

preparation, 96 

properties, 97 
dichloroethyl, 92 

dichloromethyl, 2, 3, 4, 13, 92, 284 
analysis, 98 
manufacture, 93 
preparation, 93 
properties, 94 
trichloromethyl, 95 
tetrachloromethyl, 95 
pentachloromethyl, 95 
hexachloromethyl, 95 
phenyl phenacyl, 162 
Ethers, halogenated, Chapter VII. 
B Ethoxy ethyl vinyl sulphide, 238 

B' hydroxyethyl sulphide, 238 
BB' dIEthoxy ethyl sulphide, 238, 243 
Ethyl acetate derivatives as war gases, 
117 et seq. 
arsenic acid, 283 
arsenious oxide, 283 

sulphide, 283 
benzyl ether, 130 
bromoacetate, 119 
preparation, 120 
properties, 121 



SUBJECT INDEX 



353 



Ethyl fi bromo ethyl sulphide, 215 
dibromoarsine, 273, 284 
chloroacetate, 117 

preparation, 118 

properties, 118 
j8 chloroethyl sulphide, 215 
a chloropropionate, 17 
/J chloropropionate, 17 
dichloroarsme, 2, 3, 4, 272, 279, 329, 
33i 

analysis, 329, 331 
manufacture, 281 
preparation, 280 
properties, 282, 283 
chlorosulphonate, 268 
cyanoacetate, 119 
fluorosulphonate, 255 
Ethyl lodoacetate, 121 

dnodoarsme, 283 
10 Ethyl 5 10 dihydro phenarsazme, 279 
4 Ethyl 1 4 thiazane, 239 
diEthyl ethylene thioglycol, 241 
triEthyl ammo phenyl arsonium 

chloride, 301 
tetraEthyl orthocarbonate, 171 
Ethylate test for chloropicnn, sodium, 
178 

Ethylene, tetrabromo, 51 

tetraiodo, 53 

chlorohydrin, 221 

glycol carbonate, 71 

thiodiglycol, 222, 226 
dichloroethyl ester, 216 
diEthylene disulphide, 236 

disulphone, 236 

tnsulphide, 237 
Ewin's method for the decomposition 

of the arsenical war gases, 330 
Explosion, instability of war gases to, 

14, 200 



Fermentation wash for manufacture of 

hydrocyanic acid, 184 
Ferric thiocyanate test for hydrocyanic 

acid, 204 

•* Filtchar " catalyst m phosgene 

manufacture, 64 
Flame test for chlorine, 40 

chloropicnn, 177 
Fluorescein test for bromine, 42 
Fluoride, benzyl, 128 

carbonyl, 57 

cyanogen, 181, 187 

formyl, 59 

phenarsazme, 319 
Fluorine compounds as war gases, 57, 

59, 128, 148, 155, 164, 187, 255, 266, 

3i9 

Fluoroacetone, 148 
Fluoroacetophenone, 155 
triFluoronitroso methane, 164 
Fluorosulphonate, ethyl, 255 

methyl, 255, 266 
Foodstuffs, effect of war gases on, 73, 

114 

WAR GASES. 



Fordos and Gehs's method for the 
determination of hydrocyanic acid, 
207 

Forestite (hydrocyanic acid, q v ) See 

Table XIV 
Formate, methyl, 99, 100 
manufacture, 101 
preparation, 100 
properties, 101 
Formoxime, dibromo, 21, 58 
chloro, 58, 76 
dichloro, 21, 58, 77, 165 
preparation, 77 
properties, 78 
cyano ammo chloro, 78 
duodo, 58 
Formyl fluoride, 59 

Fraisinite (benzyl iodide, q v ) See 

Table XIV 
Freezing points of the war gases, 10 
bromobenzyl cyanide, 198 fn 
dichloroethyl sulphide, 10, 223 
French method for manufacturing 

dichloroethyl sulphide, 223 fn 2 
Fulminate, mercury, 77 
Fulminuric acid, meta, 76 

Gas laws and the war gases, 33 fn 
Gaseous war gases, 8, 27 
Gay-Lussac gas law, 33 fn 
German method for manufacturing 

dichloroethyl sulphide, 220, 

221 

ethyl dichloroarsme, 281 
diphenyl chloroarsme, 306 
pharmacopoeia method for 

decomposing arsenical war gases, 
329 

Gibson and Pope's method for 

preparing dichloroethyl sulphide, 
218 et seq 

Glaser and Fritsch's test for phosgene, 
82 fn 

Glycerine, nitro, development of carbon 

monoxide, 46 
Glycerol carbonate, 72 
Glycol carbonate, 71 
Glycollic acid, 118, 121, 143 

aldehyde, 144 
Green Cross gases, 28 
Griffith's test for iron pentacarbonyl, 

54. 56 

Grignard, Rivat and Schatchard's 

method of determining dichloroethyl 

sulphide, 252 
Grignard's test for dichloroethyl 
sulphide and phenyl 
carbylamme chloride, 204, 248 
Guanidine, 170 

tnphenyl, 203 
Guignard's test for hydrocyanic acid, 

205 

Guncotton, development of carbon 

monoxide by, 46 
Guthrie's method for preparing 

dichloroethyl sulphide, 217 et seq 

12 



354 



SUBJECT INDEX 



Gutzeit-Sanger-Black method for 

analysis of arsenical war gases, 326 
Haber product for war gases, 3 
Halogen atoms in war gases, 15, 18, 

20, 23. 45 
Halogenated esters as war gases, 99 

ethers as war gases, 91 

nitro compounds as war gases, 163 
Halogenation, 137, 146, 148, 150, 156 
Halogens as war gases, Chapter IV. 
Hexamethylene tetramine compounds 

with war gases, 70, 149, 159, 162 
Hoechst plants for manufacturing 

chlorinated chloroformates, 107 
Hoffmann's method of manufacturing 

chloropicrin, 166 
Holleley's method of analysing 

dichloroethyl sulphide, 250 
Homomartonrte (bromomethyl ethyl 

ketone, q.v.). See Table XIV. 
Hoolamfte, reagent for carbon 

monoxide, 56 
Hopcalite, catalyst for oxidation of 

carbon monoxide, 47, 56 
Hopkins's potentiometric method of 

determining dichloroethyl sulphide, 

250 

HS (dichloroethyl sulphide, q.v.). See 

Table XIV. 
Hydrazine test for acrolein, p nitro 

phenyl, 144 
Hydriodic acid test for cyanogen 

bromide, 209 
Hydrochloric acid, determination in 

phosgene, 89 
Hydrocyanic acid, 8, 10, 13, 22, 45, 
181, 315 
analysis, 204, 206 
manufacture, 183 
preparation, 182 
properties, 184 
Hydrogen peroxide test for 
dichloroethyl sulphide, 247 
sulphide test for aliphatic arsines, 328 
Hydrolysis-acceleration of war gases, 

67, 227, 310 
Hydroxy methyl phenyl ketone, 158 

vinyl acetonitrile, 144 
Hypophosphorus acid reagent for ' 
arsenical war gases, 328 

Indigo test for chlorine, 40 
j'solndole, 162 

Inorganic substances as war gases, 15, 
271 

Insecticides, war gases as, 104, 165 
Insupportability, limit of, 2 
Iodide, carbonyl, 59 

dichloroethyl sulphide trichloro-, 
232 

pentachloro-, 232 
cyanogen, 22, 194 
oxalyl, 59 
phenarsazine, 319 

potassium, test for chlorine and 
bromine, 41, 42, 43 



Iodide, sodium, test for phosgene, 86 
Iodine pentoxide test for carbon 

monoxide, 55 
Iodoacetate, ethyl, 121 
Iodoacetone, 13, 147 
a Iodoacetophenone, 159 
dilodoacetylene, 22, 45, 55 
88' dilodoethyl sulphide, 215, 236, 237, 
244, 248 
diiodide, 230 

sulphone, 245 

sulphoxide, 245 
dilodoformoxime, 58 
tetralodoethylene, 53 
Iodoplatinate test for dichloroethyl 

sulphide, 246 
Iprite (dichloroethyl sulphide, q.v.). 
Iron pentacarbonyl, 47 

nonacarbonyl, 49 
Irritant war gases, lung-, 28 
Irritation, lower limit of, 2 
Isoamyl dichloroarsine, 273 
Isoindole, 162 
Isonitriles, 21, 181 
Isopropenyl chloroformate, 71 
Ivanov's method of determining 

acrolein, 145 



Jankovsky's classification of the war 

gases, 29 
Javel water, 36 

Jurecev's method for determination of 
the aliphatic arsines, 331 



Ketone, a bromoethyl methyl, 25 

8 bromoethyl methyl, 25 

bromomethyl ethyl, 153 

a chloroethyl methyl, 17 

8 chloroethyl methyl, 17 

aj8 dichloroethyl methyl, 146 

a '/J dichloroethyl methyl, 147 
Ketones, halogenated, Chapter XI. 
Kling and Schmutz's test for phosgene, 

83. 84 

Klop (chloropicrin, q.v.). See Table 
XIV. 

K Stoff (phenyl carbylamine chloride, 
q.v.). See Table XIV. 



Labarraque water, 36 
Labyrinthic gases, 92 
Lacrimite (thiophosgene, q.v.). See 

Table XIV. 
Lethal index of war gases, 3 
Levinstein's method for the 

manufacture of dichloroethyl 

sulphide, 223 
Lewin's tests for acrolein, 144 
Lewisite (chlorovinyl dichloroarsine, 

q.v.). See Table XV. 
Liebig's test for hydrocyanic acid, 206 
Liquid war gases, 10, 27 
Lob's test for benzyl chloride, 138 



SUBJECT INDEX 



355 



Lost (dichloroethyl sulphide, q v.). See 

Table XIV. 
Lubricating oil treatment with 

dichloromethyl ether, 96 
Lung irritant gases, 28 



Mi (chlorovmyl dichloroarsme, qv). 

See Table XV. 
Martonite (bromoacetone and 

chloroacetone) , 153 
Mauguinite (cyanogen chloride, q v ) 

See Table XIV 
Maxim's method for the determination 

of dichloroethyl sulphide, 250 
MD (methyl dichloroarsme, q v ) See 

Table XIV 
Melting points of the war gases, 10 
Mercaptan, chloroethyl chloro, 235 
perchloromethyl, 211 
cyanobenzyl, 200 
Mercaptans as war gases, 211 
Mercurichloride, phenyl, 298 
Mercuriiodide test for dichloroethyl 

sulphide, potassium, 247 
Mercurous chloride addition product 

with dichloroethyl sulphide, 241 
Mercury fulminate, 77 
Metafulminuric acid, 76 
Metals, effect of war gases on, 14, 35, 
40, 72, 80, 96, 114, i2i ( 132, 134, 
138, 144, 150, 153, 160, 172, 187, 
190, 194, 200, 204, 213, 241, 261, 
265, 269, 279, 284, 293, 302, 313, 326 
Meteorological conditions and war 

gases, 33, 199 
Methane, tribromo nitro, 174 
dichloro dmitro, 78 
trichlorodmitro hydroxy, 174 
tnchloronitroso, 77, 164 
tnfluoronitroso, 164 
tnsulphonic acid, 171 
Methoxy phenarsazme, 325 
Methylal, dimethyl, 96 
Methylamine, 170, 186 
Methyl arsenic acid, 278 
arsenimide, 278 
arsenious sulphide, 278 
chlorocarbonate, 99 
a chloroethyl ketone, 146 
chloroformate, 10 1 
analysis, 104 
manufacture, 102 
preparation, 102 
properties, 103 
chlorosulphonate, 258, 262, 266, 269 
analysis, 269 
preparation, 267 
properties, 267 
dichloroarsme, 6, 7, 20, 273, 329, 
331, 332 
analysis, 329, 331, 332 
manufacture, 275 
preparation, 274 
properties, 276 
<xj8 dichloroethyl ketone, 146 



Methyl tetrachloroarsme, 277 
cyanoformate, 103, 104 
dicyanoarsme, 273 
Dick (methyl dichloroarsme, q v ) 

See Table XIV 
fluorosulphonate, 255, 266 
formate, 99, 100 
manufacture, 10 1 
preparation, 100 
properties, 101 
mercaptan tnsulphonic acid, 214 
sulphuric acid, 261 
4 Methyl 1 4 thiazane, 239 
Methyl thiocyanate, 211 
diMethyl ammo benzaldehyde and 
diphenylamme test for phosgene, 
81 

aniline test for chloropicrm, 178 
bromoarsme, 273 
carbonate, 71 
chloroarsme, 273 
fluoroarsme, 273 
methylal, 96 
peroxide, 265 
sulphate, 262, 269 

analysis, 269 

manufacture, 264 

preparation, 263 

properties, 264 
hexaMethylene tetramine compounds, 

70, 149 159, 162 
Meyer's method of preparing 

dichloroethyl sulphide, 218, 220 

el seq 

theory of structure of war gases, 23 
Michler's ketone, 70 
Mines apparatus, safety in, 55 
Mortality product, 2, 3 
Mustard gas See Dichloroethyl 

sulphide 

Myers and Stephen's method of 
preparing dichloroethyl sulphide, 219 

Naphthalene compounds as war gases, 
298 

/5 Naphthol test for dichloroethyl 

sulphide, 246 
Naphthyl methyl chloroarsme, 298 

fluoroarsme, 298 
NC (chloropicrm and stannic chloride), 

169 

Negroes, action of dichloroethyl 

sulphide on, 242 
Nickel tetracarbonyl, 44, 49 
Nierenstein's test for acrolein, 144 
Nitrate group, biological effect, 20 

test for carbon monoxide, silver, 53 
Nitrile, /3 chloropropio , 239 

a hydroxy vinyl aceto , 144 

group, iso , 21, 181 
Nitriles as war gases, 21, 181 
0 Nitrobenzyl chloride, 21, 135 
m Nitro a chloroacetophenone, 158 
Nitro-compounds, halogenated, 

Chapter XII, 135 
Nitroglycerine, 46 



356 



SUBJECT INDEX 



Nitro group m war gases, 20, 23 
Nitromethane disulphonic acid, 171 
p Nitrophenyl hydrazine test 

for acrolein, 144 
Nitroso-dimethyl ammophenol, 81 
Nitrosyl bromide, 175 
Nitro tnthioformic esters (ortho), 172 
tetraNitro ethane (salts), 174, 175 

Odour, detection of war gases by, 

40, 57. 81, 176 
Orticant action of war gases, 21, 147, 

155, 161, 217 
Oxalanilide, 80 
Oxalyl bromide, 59 

chloride, 59, 79 

iodide, 59 
Oxamide, 186 

Oxide, chlorovmyl arsenious, 291 

dichlorovmyl arsenious, 294 

trichlorovmyl arsenic, 296 

ethyl arsenious, 283 

phenarsazme, 323, 324 
Oxime group m war gases, 21 
Oxygen atom in war gases, 23 



Paints, penetration of dichloroethyl 

sulphide, 226 
Palite (mono- and dichloromethyl 

chloroformates) , 104 
Palladium test for carbon monoxide. 54 
Pancenko's method of analysing 

trichloromethyl chloroformate, 125 
Papite (acrolein, q v ) See Table XIV 
Paracyanogen, 188 
Particulate smokes, 272, 327 fn 
Pathological action of phosgene, 74 
Perchloromethyl mercaptan, 211 
Permanganate test for dichloroethyl 

sulphide, 246 
Peroxide, methyl, 265 

test for chloropicrm sodium, 180 
Persistence of the war gases, 10, 28, 

244 

Perstoff (trichloromethyl 

chloroformate, q v ) See Table XIV 
Petroleum as raw material for 

chloropicrm, 167 
Pferffer process for manufacturing 

bromine, 38 
Phenacyl aniline, 159 

phenyl ether, 229 

sulphide, 159, 162 

thiocyanate, 160 

thiosulphate, 160 
Phenarsazine bromide, 319 

chloride. 318, 319, 320, 329, 335 
analysis, 329, 335 
manufacture, 321 
preparation, 320 
properties, 322 

cyanide, 181, 319, 325 

fluoride, 319 

iodide, 319 

oxide, 323, 324 



triPhenarsazme amine, 324 

chloride, 326 
Phenarsazine, 10 chloro 5 10 dihydro 
(phenarsazme chloride, q v ) 
10 ethyl 5 10 dihydro, 279 
methoxy, 325 
Phenarsazines, alkyl, 326 

aryl, 326 
Phenarsazinic acid, 325 
Phenazine, 318 
Phenol test for bromine, 42 

for phosgene, nitroso dimethyl 
ammo, 81 
Phenoxarsine chloride, 319 
Phenoxazine, 318 
Phenyl anilmo chloroarsme, 300 
arsenimide, 300 
arsenious acid, 300 
oxide, 300 

(dttner), 299 
sulphide, 301 
arsenites, 300 
cacodyl, 313 

carbylamme chloride, 200 
manufacture, 202 
preparation, 201 
properties, 203 
/J chloro vmyl chloroarsme, 286 
dichloroarsme, 19, 20, 298, 326, 333 
analysis, 326, 333 
preparation, 298 
properties, 299 
trichloromethyl carbonate, 113 
isocyanate, 203 
isothiocyanate, 201, 202, 203 
dicyanoarsme, 301 
mercunchlonde, 299 
phenacyl ether, 162 
4 Phenyl 1 4 thiazane, 239 
Phenyl thioarsane, 240 

dithiocarbamate, calcium, 201 
diPhenyl arsenic acid, 311, 313, 317 
hydrochloride, 311 
nitrate, 311 
sulphate, 311 
arsenimide, 310 
arsenious oxide, 310, 316 
sulphide, 311 
thiocyanate, 312 
bromoarsme, 314 
tribromoarsme, 314 
carbonate, 113 

chloroarsine, 2, 3, 4, 6, 7, 17, 19, 20, 
302, 326, 333 

analysis, 326, 333 

manufacture, 304 

preparation, 303 

properties, 308 

bromide, 310 

perbromide, 311 
tnchloroarsme, 310 
cyanoarsme, 7, 20, 314, 326, 334 

analysis, 326, 334 

manufacture, 316 

preparation, 315 

properties, 316 



SUBJECT INDEX 



357 



diPhenyl wdoareme, 311, 312 
dimethyl arsonium iodide, 317 

trnodide, 312, 317 
urea, 69, 82, 83 et seq 
triPhenyl arsine, 19, 298, 302, 303, 305 

guamdine, 203 
tetraPhenyl diarsme, 312, 313 

tetrachloroarsenic anhydride, 317 
diPhenylamine chloroarsme See 

Phenarsazme chloride 
Phosgene, 2, 4, 6, 8, 10, 11, 12, 27, 28, 
3°. 3i. 57. 59, 81, 83, 87, 88, 89 
analysis, 81, 83, 87, 88, 89 
manufacture, 62 
preparation, 60 
properties, 65 
bromo, 74 

preparation, 75 
properties, 75 
bromochloro, 69 
di- See Tnchloromethyl 

chloroformate 
tn See Hexachloromethyl 
carbonate 
Physical classification of the war 
gases, 27 
properties of the war gases, 1, 4 
Physiopathological classification of the 
war gases, 28 
properties of the war gases, 1, 15 et 
seq 

of dichloroethyl sulphide, 242 
of lachrymators, 3 
of phosgene, 74 
of sternutators 3 
Picric acid, 46, 166, 167, 174, 175 

sodium salt, test for hydrocyanic 
acid, 205 

Polymerisation, 13, 143, 149, 183, 190, 
237 

Potassium iodide test for bromine , 42, 43 
for chlorine, 41 
mercurnodide test for dichloroethyl 

sulphide, 246 
permanganate test for dichloroethyl 
sulphide, 246 
Powder, black, 46 

Pressure of the war gases, vapour, 4 
Projectiles, corrosion by war gases, 14 
jsoPropenyl chloroformate, 71 
Properties desired m war gases, 33 

of the war gases, general, Chapter I 
Propionate, ethyl « chloro, 17 

j8 chloro, 17 
Propyl chlorosulphonate, 255 
Protection of projectiles, 14 
Prussian blue reaction for cyanogen 

compounds, 190, 195, 204 
PS (chloropicrm, q v ) See Table XIV. 



Rationite (dimethyl sulphate and 

chlorosulphonic acid), 262 
Ray and Das's test for chloropicrm, 172, 

177 

Resorcinol test for chloropicrm, 179 



Resorufin test for bromine, 42 
Robertson's method for analysis of 

arsenical war gases, 330 
Rogers's method for analysis of 

arsenical war gases, 331 
Rubber, action of bromobenzyl 
cyanide on, 200 
of carbonyl bromide on, 75 
of dichloroethyl sulphide on, 225 
of dichloroformoxime on, 79 
of tnchloronitroso methane on, 
165 

of hydrocyanic acid on, 185 
of methyl fluorosulphonate on, 266 
of phosgene on, 72 
Rumanian method for manufacture of 
chloropicrm, 167 



Schiff's reaction for bromine, 42 
SchrSter's test for dichloroethyl 

sulphide, 248 
Schulze's analytical method for benzyl 

chloride, 138 
Schuttzenberger and Gngnard's method 

for manufacturing phosgene, 62 
Selenide, dichloroethyl, 217 
Selenious acid reagent for 

dichloroethyl sulphide, 233, 247, 249 
Selenium compounds as war gases, 217 
1 4 Selenothiane, 240 
Semi-persistent war gases, 28 
Senf gas See Dichloroethyl sulphide 
Sensitivity, threshold of pathological, 2 
Ships, dismfestation of, by chloropicrm, 

165 

Silver nitrate test for carbon monoxide, 
53 

SK (ethyl lodoacetate, q v ) See Table 
XIV 

Smokes, particulate, 272, 313 
Sodium arsenite test for cyanogen 
iodide, 209 
ethylate test for chloropicrm, 178 
iodide test for phosgene, 86 
lodoplatmate test for dichloroethyl 

sulphide, 246 
peroxide test for chloropicrm, 180 
sulphide test for dichloroethyl 

sulphide, 247 
sulphite test for chloropicrm, 179 
Solid war gases, 27 

Spectroscopic test for carbon monoxide, 
54 

Stabilisers for war gases, 13, 143, 183 
Stannic chloride compound with 

hydrocyanic acid, 187 
Stassfurt salts as raw materials for 

bromine manufacture, 38 
Steinkopf s method of preparing 

dichloroethyl sulphide, 219 
Sternite (phenyl dichloroarsme and 

diphenyl chloroarsme) , 302 
Stibine as war gas, 15 

diphenyl chloro, 297 
cyano, 297 



358 SUBJECT 

Stilbene, dicyano, 199 

Structure of war gas molecules, 

Chapter II. 
Styryl dichloroarsine, fi chloro, 285 
Sulphamide, 259 
Sulphanilic acid, 269 
Sulphate, Pp' dichloroethyl, 261 
dichloromethyl, 95, 255, 257 
methyl hydrogen, 261 
dimethyl, 262, 269 
analysis, 269 
manufacture, 264 
preparation, 263 
properties, 264 
Sulphide war gases, 214 et seq. 
diacetonyl, 149 
benzyl, 132 

p bromoethyl ethyl, 215 

PP' dibromoethyl, 16, 18, 215, 243 

preparation, 243 

properties, 243 
P chloroethyl ethyl, 215 

vinyl, 238 
chloromethyl, 215 
P chlorovinyl arsenious, 292 
a chlorovinyl p' chloroethyl, 234 
p chlorovinyl p' chloroethyl, 234 
dichloroacetyl, 216 
pp' dichlorobutyl, 215 
SS' dichlorobutyl, 216 
aa' dichloroethyl, 25, 215 
jiff dichloroethyl, 6, 7, 8, 10, 11, 12, 
13, 16, 18, 25, 27, 28, 30, 31, 
215, 216, 217, 246, 249, 250 

analysis, 246, 249, 250 

manufacture, 220 

preparation, 217 

properties (physical), 223 
(chemical), 226 
<xj8 dichloroethyl vinyl, 237 
pp' dichloropropyl, 215 
yy' dichloropropyl, 216 
dichlorovinyl diarsenious, 295 
O.PP' trichloroethyl, 233 
aa'pp' tetrachloroethyl, 237 
aPPp' tetrachloroethyl, 233 
PP'yy' tetrachloropropyl, 216 
aaa PP' pentachloroethyl, 235 
aaa'pP'P' hexachloroethyl, 235 • 
axtpppp' hexachloroethyl, 233 
aaa PPP'P' heptachloroethyl, 235 
dicyanobenzyl, 199 
P ethoxy ethyl vinyl, 238 

p' hydroxyethyl, 238 
PP' diethoxy ethyl, 238, 243 
ethyl arsenious, 283 
PP' diiodoethyl, 215, 236, 237, 244, 

248 

methyl arsenious, 278 
phenacyl, 159, 162 
diphenyl arsenious, 311 
dibromide, PP' dichloroethyl, 230 
tetrabromide, PP' dichloroethyl, 
230 

dichloride, pp' dichloroethyl, 230, 
231. 234 



INDEX 

Sulphide trichloroiodide, pp' 
dichloroethyl, 232 
pentachloroiodide, PP' dichloroethyl, 

232 

test for aliphatic arsines, hydrogen, 
328 

for dichloroethyl sulphide, sodium, 
247 

diSulphide, diethylene, 236, 247 
diSulphides, alkyl, 172 
triSulphide, diethylene, 237 
SulphiUmine group, 232 
Sulphite test for chloropicrin, sodium, 
179 

Sulphone, pp' dibromoethyl, 244 

PP' dichloroethyl, 228, 229 

pp' diiodoethyl, 245 
diSulphone, ethylene, 236 
diSulphonic acid, nitromethane, 171 
triSulphonic acid, methane, 171 

methyl mercaptan, 214 
Sulphonic anhydride, trichloromethyl, 

212 

Sulphoxide, pp' dibromoethyl, 244 
PP' dichloroethyl - , 228, 229, 231, 
234 

aa'pp' tetrachloroethyl, 232 
PP' diiodoethyl, 245 
Sulphur atom in war gases, effect on 
properties, 17 
compounds as war gases, Chapter 
XIV. 

Sulphuric acid, methyl, 261 

esters, 253 
Sulphury! chloride, 258, 269, 270 
analysis, 269, 270 
preparation, 258 
properties, 259 
Sulvinite (ethyl chlorosulphonate, 

q.v.). See Table XIV. 
Surpalite (trichloromethyl 

chloroformate, q.v.) . See Table XIV. 
Symmetry of war gas molecules, 22 



Telluride, dichloroethyl, 217 
Tension of war gases, vapour, 4 
Textiles, effect of war gases on, 153, 

225, 233, 265, 317 
Theories of relation between structure 

and action of war gases, 23 
1.4 Thiazane, 239 

4 ethyl, 239 

4 methyl, 239 

4 phenyl, 239 

derivatives, 239, 244 
Thioarsane, phenyl, 240 
diThiocarbamate, calcium phenyl, 201 
Thiocarbanilide, 201 
Thiocyanate, methyl, 211 

phenacyl, 160 
zsoThiocyanate, phenyl, 201, 202, 203 
Thiocyanate, diphenyl arsenious, 312 

test for iron pentacarbonyl, 204 
Thiodiglycol, ethylene, 218, 222, 226 
Thioethers as war gases, 214 et seq. 



SUBJECT INDEX 



359 



Thioglycol dichloroethyl ester, 
ethylene, 216 

diethyl ethylene, 241 
Tniophenol test for chloropicrin, 1 78 
Thiopho»gene, 211, 212, 213 

manufacture, 214 

preparation, 213 

properties, 214 
diThiophosgene, 214 
Thiosulphate, phenacyl sodium, 160 

sodium cyanobenzyl, 199 
p Thioxane, 236 

Thymol test for chloropicrin, 1 79 
Tin chloride (stannic), 187 

(stannous), 241 
Titanium chloride, 187, 241 
T.N.T., 46 

Toluene, monobromo, 17 
dlTolyl chloroarsine, 20 
Tonite (chloroacetone, q.v.). See Table 
XIV. 

Toxic smokes, 272, 313 

war gases, 28, 29 
Toxic-suffocant (lung irritant) war 

gases, 28 
Toxicity of war gases, 2, 3 
Toxophor-Auxotox theory of the war 

gases, 24, 29 
Toxophors, 24, 29 

T Stoff (benzyl bromide, xylyl bromide, 
q.v.). See Table XIV. 



Unsaturation in the molecules of war 
gases, 22 

Urea, diphenyl, 69, 82, 83 et seq., 113 
Urethane, N chloroacetyl, 119 

trichloromethyl N diphenyl, 113 
Urotropine. See Hexamethylene 

tetramine. 



Van der Laan's analysis method for 

benzyl bromide, 139 
Vapour tension of war gases, 4 
Vesicant gases, 18, 22, 28 
Villantlte (methyl chlorosulphonate, 

q.v.). See Table XIV. 
Vincennite, 185 

Vivrite (cyanogen chloride and arsenic 

trichloride), 188 
Volatility of the war gases, 6, 9 



War gases : 

action, delayed biological, 242 
on blondes, 242 
on brunettes, 242 
on building materials, 225 
on cork, 266 
on foodstuffs, 73, 1 14 
on metals. See Metals, 
on negroes, 242 

on rubber, 72, 75, 79, 165, 185, 

200, 225, 266 
on textiles, 225, 233, 265, 317 



War gases — contd. 

adsorption by alumina, 50 

by carbon, 44, 73, 114, 173, 180, 317 
by silica gel, 327 fn. 1, 331 
aerosols as, 297, 313, 327 fn. 1 
analysis, qualitative chemical, 40, 
53. 81. 98, 123, 138, 144, 176, 
204, 246, 269, 326 
by odour, 40, 81, 176 
quantitative, 42, 55, 83, 98, 124, 
145, 179, 206, 249, 270, 329 
antigas niters for (and see Adsorption 

by carbon) , 68, 70 
arsenic atom in, 18, 319 et seq. 
biological action. See Chapters I 
and II. 
irritant, 2, 28 
labyrinthic, 92 
lachrymatory, 2, 3, 16 et seq. 
lung irritant, 28 
orticant, 21, 147, 155, 161, 217 
toxic, 3, 21, 29 
suffocant, 28 
vesicant, 17 et seq., 28, 58, 59. 
242, 279, 284, 293, 295, 297, 
302, 313 
blondes, action on, 242 
brunettes, action on, 242 
carbonyl group in, 23, 24 
classification, biological, 28 
chemical, 29 
Chugaev, 29 
Engel, 32 
Jankovsky, 29 
Zitovic, 29 
chronological, Table XIV and p. 32 
military, 27 
physical, 27 
physiopathological, 28 
corrosive action on metals. See 
Metals. 

cyanide group in, 20, 21, 24, 

Chapter XIII. 
decontamination, 13, 36, 73, 153, 

154, 231, 232, 233, 242, 284 
explosion-stability, 14, 200, 325 
halogen atom in, 15, 23, 45 
inorganic, 15, 271 
labyrinthic, 92 
lachrymatory, 2, 3, 16 et seq. 
lung irritant (toxic-suffocant), 28 
meteorological conditions and, io, 

11, 12, 33 
military nomenclature. See Tables 

XIV, XV. 
molecular symmetry of, 22 
negroes, action on, 242 
nitrate group in, 21 
nitro group in, 21, 23 
number used, vii 
orticant, SI, 147, 155, 161, 217 
oxime group in, 21 
oxygen atom in, 23 
peacetime uses of, 96, 165, 262 
penetration into building materials, 

etc., 225 



360 SUBJEC 

War gases — contd. 

persistence, 10, 28, 244 
polymerisation, 13, 143, 149, 183, 
190,237 

properties, biological, 1, 15 et seq., 24 
chemical, 1 and passim 
desired, 33 

physiopathological, 1, 15 et seq., 24 
shell markings for, 28 
stabilisation, 13, 143, 183, 190 
stability, 12, 13, 14, 17, 59, 200, 325 
storage, 13, 143 
sulphur atom in, 17 
toxophor-auxotox theory of, 24 
unsaturation in, 22 
vesicant, 17 et seq., 28, 58, 59, 242, 

279, 284, 293, 295, 297, 302, 313 

Xylyl bromide, 13, 14, 136 
analysis, 138 



INDEX 

Xylyl bromide, manufacture, 137 

preparation, 137 

properties, 138 
Xylylene bromide, 136 



Yablich's reagent for dichloroethyl 

sulphide, 247 
Yant's test for phosgene, 84 
Yellow Cross gases, 28 
Yp&ite. See Dichloroethyl sulphide. 



Zinc chloride compound with 

hydrocyanic acid, 187 
Zftovic's classification of the war 

gases, 29 
Zyklon, A, 104 

B, 104, 190 



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